Elixir v1.4.5 Enum View Source
Provides a set of algorithms that enumerate over enumerables according
to the Enumerable
protocol.
iex> Enum.map([1, 2, 3], fn(x) -> x * 2 end)
[2, 4, 6]
Some particular types, like maps, yield a specific format on enumeration.
For example, the argument is always a {key, value}
tuple for maps:
iex> map = %{a: 1, b: 2}
iex> Enum.map(map, fn {k, v} -> {k, v * 2} end)
[a: 2, b: 4]
Note that the functions in the Enum
module are eager: they always
start the enumeration of the given enumerable. The Stream
module
allows lazy enumeration of enumerables and provides infinite streams.
Since the majority of the functions in Enum
enumerate the whole
enumerable and return a list as result, infinite streams need to
be carefully used with such functions, as they can potentially run
forever. For example:
Enum.each Stream.cycle([1, 2, 3]), &IO.puts(&1)
Link to this section Summary
Functions
Returns true if the given fun
evaluates to true on all of the items in the enumerable
Returns true if the given fun
evaluates to true on any of the items in the enumerable
Finds the element at the given index
(zero-based)
Shortcut to chunk(enumerable, count, count)
Returns list of lists containing count
items each, where
each new chunk starts step
elements into the enumerable
Splits enumerable on every element for which fun
returns a new
value
Given an enumerable of enumerables, concatenates the enumerables into a single list
Concatenates the enumerable on the right with the enumerable on the left
Returns the size of the enumerable
Returns the count of items in the enumerable for which fun
returns
a truthy value
Enumerates the enumerable
, returning a list where all consecutive
duplicated elements are collapsed to a single element
Enumerates the enumerable
, returning a list where all consecutive
duplicated elements are collapsed to a single element
Drops the amount
of items from the enumerable
Returns a list of every nth
item in the enumerable dropped,
starting with the first element
Drops items at the beginning of the enumerable while fun
returns a
truthy value
Invokes the given fun
for each item in the enumerable
Determines if the enumerable is empty
Finds the element at the given index
(zero-based)
Finds the element at the given index
(zero-based)
Filters the enumerable, i.e. returns only those elements
for which fun
returns a truthy value
Filters the enumerable and maps its elements in one pass
Returns the first item for which fun
returns a truthy value.
If no such item is found, returns default
Similar to find/3
, but returns the index (zero-based)
of the element instead of the element itself
Similar to find/3
, but returns the value of the function
invocation instead of the element itself
Returns a new enumerable appending the result of invoking fun
on
each corresponding item of enumerable
Maps and reduces an enumerable, flattening the given results (only one level deep)
Splits the enumerable into groups based on key_fun
Intersperses element
between each element of the enumeration
Inserts the given enumerable
into a collectable
Inserts the given enumerable
into a collectable
according to the
transformation function
Joins the given enumerable into a binary using joiner
as a
separator
Returns a list where each item is the result of invoking
fun
on each corresponding item of enumerable
Returns a list of results of invoking fun
on every nth
item of enumerable
, starting with the first element
Maps and joins the given enumerable in one pass
Invokes the given function to each item in the enumerable to reduce it to a single element, while keeping an accumulator
Returns the maximal element in the enumerable according to Erlang’s term ordering
Returns the maximal element in the enumerable as calculated by the given function
Checks if element
exists within the enumerable
Returns the minimal element in the enumerable according to Erlang’s term ordering
Returns the minimal element in the enumerable as calculated by the given function
Returns a tuple with the minimal and the maximal elements in the enumerable according to Erlang’s term ordering
Returns a tuple with the minimal and the maximal elements in the enumerable as calculated by the given function
Returns a random element of an enumerable
Invokes fun
for each element in the enumerable
, passing that
element and the accumulator as arguments. fun
’s return value
is stored in the accumulator
Invokes fun
for each element in the enumerable
, passing that
element and the accumulator acc
as arguments. fun
’s return value
is stored in acc
Reduces the enumerable until fun
returns {:halt, term}
Returns elements of enumerable
for which the function fun
returns
false
or nil
Returns a list of elements in enumerable
in reverse order
Reverses the elements in enumerable
, appends the tail, and returns
it as a list
Reverses the enumerable in the range from initial position start
through count
elements
Applies the given function to each element in the enumerable, storing the result in a list and passing it as the accumulator for the next computation
Applies the given function to each element in the enumerable,
storing the result in a list and passing it as the accumulator
for the next computation. Uses the given acc
as the starting value
Returns a list with the elements of enumerable
shuffled
Returns a subset list of the given enumerable, from range.first
to range.last
positions
Returns a subset list of the given enumerable, from start
position with amount
of elements if available
Sorts the enumerable according to Erlang’s term ordering
Sorts the enumerable by the given function
Sorts the mapped results of the enumerable according to the provided sorter
function
Splits the enumerable
into two enumerables, leaving count
elements in the first one
Splits enumerable in two at the position of the element for which
fun
returns false
for the first time
Splits the enumerable
in two lists according to the given function fun
Returns the sum of all elements
Takes the first count
items from the enumerable
Returns a list of every nth
item in the enumerable,
starting with the first element
Takes count
random items from enumerable
Takes the items from the beginning of the enumerable while fun
returns
a truthy value
Converts enumerable
to a list
Enumerates the enumerable
, removing all duplicated elements
Enumerates the enumerable
, by removing the elements for which
function fun
returned duplicate items
Opposite of Enum.zip/2
; extracts a two-element tuples from the
enumerable and groups them together
Returns the enumerable with each element wrapped in a tuple alongside its index
Zips corresponding elements from a collection of enumerables into one list of tuples
Zips corresponding elements from two enumerables into one list of tuples
Link to this section Types
Link to this section Functions
Returns true if the given fun
evaluates to true on all of the items in the enumerable.
It stops the iteration at the first invocation that returns false
or nil
.
Examples
iex> Enum.all?([2, 4, 6], fn(x) -> rem(x, 2) == 0 end)
true
iex> Enum.all?([2, 3, 4], fn(x) -> rem(x, 2) == 0 end)
false
If no function is given, it defaults to checking if all items in the enumerable are truthy values.
iex> Enum.all?([1, 2, 3])
true
iex> Enum.all?([1, nil, 3])
false
Returns true if the given fun
evaluates to true on any of the items in the enumerable.
It stops the iteration at the first invocation that returns a truthy value (not false
or nil
).
Examples
iex> Enum.any?([2, 4, 6], fn(x) -> rem(x, 2) == 1 end)
false
iex> Enum.any?([2, 3, 4], fn(x) -> rem(x, 2) == 1 end)
true
If no function is given, it defaults to checking if at least one item in the enumerable is a truthy value.
iex> Enum.any?([false, false, false])
false
iex> Enum.any?([false, true, false])
true
Finds the element at the given index
(zero-based).
Returns default
if index
is out of bounds.
A negative index
can be passed, which means the enumerable
is
enumerated once and the index
is counted from the end (e.g.
-1
finds the last element).
Note this operation takes linear time. In order to access
the element at index index
, it will need to traverse index
previous elements.
Examples
iex> Enum.at([2, 4, 6], 0)
2
iex> Enum.at([2, 4, 6], 2)
6
iex> Enum.at([2, 4, 6], 4)
nil
iex> Enum.at([2, 4, 6], 4, :none)
:none
Shortcut to chunk(enumerable, count, count)
.
Returns list of lists containing count
items each, where
each new chunk starts step
elements into the enumerable.
step
is optional and, if not passed, defaults to count
, i.e.
chunks do not overlap.
If the final chunk does not have count
elements to fill the chunk,
elements are taken as necessary from leftover
if it was passed.
If leftover
is passed and does not have enough elements to fill the
chunk, then a partial chunk is returned with less than count
elements. If leftover
is not passed at all or is nil
, then the
partial chunk is discarded from the result.
If count
is greater than the number of elements in the enumerable
and leftover
is not passed, empty list will be returned.
Examples
iex> Enum.chunk([1, 2, 3, 4, 5, 6], 2)
[[1, 2], [3, 4], [5, 6]]
iex> Enum.chunk([1, 2, 3, 4, 5, 6], 3, 2)
[[1, 2, 3], [3, 4, 5]]
iex> Enum.chunk([1, 2, 3, 4, 5, 6], 3, 2, [7])
[[1, 2, 3], [3, 4, 5], [5, 6, 7]]
iex> Enum.chunk([1, 2, 3, 4], 3, 3, [])
[[1, 2, 3], [4]]
iex> Enum.chunk([1, 2, 3, 4], 10)
[]
iex> Enum.chunk([1, 2, 3, 4], 10, 10, [])
[[1, 2, 3, 4]]
Splits enumerable on every element for which fun
returns a new
value.
Returns a list of lists.
Examples
iex> Enum.chunk_by([1, 2, 2, 3, 4, 4, 6, 7, 7], &(rem(&1, 2) == 1))
[[1], [2, 2], [3], [4, 4, 6], [7, 7]]
Given an enumerable of enumerables, concatenates the enumerables into a single list.
Examples
iex> Enum.concat([1..3, 4..6, 7..9])
[1, 2, 3, 4, 5, 6, 7, 8, 9]
iex> Enum.concat([[1, [2], 3], [4], [5, 6]])
[1, [2], 3, 4, 5, 6]
Concatenates the enumerable on the right with the enumerable on the left.
This function produces the same result as the Kernel.++/2
operator
for lists.
Examples
iex> Enum.concat(1..3, 4..6)
[1, 2, 3, 4, 5, 6]
iex> Enum.concat([1, 2, 3], [4, 5, 6])
[1, 2, 3, 4, 5, 6]
Returns the count of items in the enumerable for which fun
returns
a truthy value.
Examples
iex> Enum.count([1, 2, 3, 4, 5], fn(x) -> rem(x, 2) == 0 end)
2
Enumerates the enumerable
, returning a list where all consecutive
duplicated elements are collapsed to a single element.
Elements are compared using ===
.
If you want to remove all duplicated elements, regardless of order,
see uniq/1
.
Examples
iex> Enum.dedup([1, 2, 3, 3, 2, 1])
[1, 2, 3, 2, 1]
iex> Enum.dedup([1, 1, 2, 2.0, :three, :"three"])
[1, 2, 2.0, :three]
Enumerates the enumerable
, returning a list where all consecutive
duplicated elements are collapsed to a single element.
The function fun
maps every element to a term which is used to
determine if two elements are duplicates.
Examples
iex> Enum.dedup_by([{1, :a}, {2, :b}, {2, :c}, {1, :a}], fn {x, _} -> x end)
[{1, :a}, {2, :b}, {1, :a}]
iex> Enum.dedup_by([5, 1, 2, 3, 2, 1], fn x -> x > 2 end)
[5, 1, 3, 2]
Drops the amount
of items from the enumerable.
If a negative amount
is given, the amount
of last values will be dropped.
The enumerable
is enumerated once to retrieve the proper index and
the remaining calculation is performed from the end.
Examples
iex> Enum.drop([1, 2, 3], 2)
[3]
iex> Enum.drop([1, 2, 3], 10)
[]
iex> Enum.drop([1, 2, 3], 0)
[1, 2, 3]
iex> Enum.drop([1, 2, 3], -1)
[1, 2]
drop_every(t, non_neg_integer) :: list
Returns a list of every nth
item in the enumerable dropped,
starting with the first element.
The first item is always dropped, unless nth
is 0.
The second argument specifying every nth
item must be a non-negative
integer.
Examples
iex> Enum.drop_every(1..10, 2)
[2, 4, 6, 8, 10]
iex> Enum.drop_every(1..10, 0)
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
iex> Enum.drop_every([1, 2, 3], 1)
[]
Drops items at the beginning of the enumerable while fun
returns a
truthy value.
Examples
iex> Enum.drop_while([1, 2, 3, 2, 1], fn(x) -> x < 3 end)
[3, 2, 1]
Invokes the given fun
for each item in the enumerable.
Returns :ok
.
Examples
Enum.each(["some", "example"], fn(x) -> IO.puts x end)
"some"
"example"
#=> :ok
Determines if the enumerable is empty.
Returns true
if enumerable
is empty, otherwise false
.
Examples
iex> Enum.empty?([])
true
iex> Enum.empty?([1, 2, 3])
false
Finds the element at the given index
(zero-based).
Returns {:ok, element}
if found, otherwise :error
.
A negative index
can be passed, which means the enumerable
is
enumerated once and the index
is counted from the end (e.g.
-1
fetches the last element).
Note this operation takes linear time. In order to access
the element at index index
, it will need to traverse index
previous elements.
Examples
iex> Enum.fetch([2, 4, 6], 0)
{:ok, 2}
iex> Enum.fetch([2, 4, 6], -3)
{:ok, 2}
iex> Enum.fetch([2, 4, 6], 2)
{:ok, 6}
iex> Enum.fetch([2, 4, 6], 4)
:error
Finds the element at the given index
(zero-based).
Raises OutOfBoundsError
if the given index
is outside the range of
the enumerable.
Note this operation takes linear time. In order to access the element
at index index
, it will need to traverse index
previous elements.
Examples
iex> Enum.fetch!([2, 4, 6], 0)
2
iex> Enum.fetch!([2, 4, 6], 2)
6
iex> Enum.fetch!([2, 4, 6], 4)
** (Enum.OutOfBoundsError) out of bounds error
Filters the enumerable, i.e. returns only those elements
for which fun
returns a truthy value.
See also reject/2
.
Examples
iex> Enum.filter([1, 2, 3], fn(x) -> rem(x, 2) == 0 end)
[2]
Filters the enumerable and maps its elements in one pass.
Examples
iex> Enum.filter_map([1, 2, 3], fn(x) -> rem(x, 2) == 0 end, &(&1 * 2))
[4]
Returns the first item for which fun
returns a truthy value.
If no such item is found, returns default
.
Examples
iex> Enum.find([2, 4, 6], fn(x) -> rem(x, 2) == 1 end)
nil
iex> Enum.find([2, 4, 6], 0, fn(x) -> rem(x, 2) == 1 end)
0
iex> Enum.find([2, 3, 4], fn(x) -> rem(x, 2) == 1 end)
3
Similar to find/3
, but returns the index (zero-based)
of the element instead of the element itself.
Examples
iex> Enum.find_index([2, 4, 6], fn(x) -> rem(x, 2) == 1 end)
nil
iex> Enum.find_index([2, 3, 4], fn(x) -> rem(x, 2) == 1 end)
1
Similar to find/3
, but returns the value of the function
invocation instead of the element itself.
Examples
iex> Enum.find_value([2, 4, 6], fn(x) -> rem(x, 2) == 1 end)
nil
iex> Enum.find_value([2, 3, 4], fn(x) -> rem(x, 2) == 1 end)
true
iex> Enum.find_value([1, 2, 3], "no bools!", &is_boolean/1)
"no bools!"
Returns a new enumerable appending the result of invoking fun
on
each corresponding item of enumerable
.
The given function must return an enumerable.
Examples
iex> Enum.flat_map([:a, :b, :c], fn(x) -> [x, x] end)
[:a, :a, :b, :b, :c, :c]
iex> Enum.flat_map([{1, 3}, {4, 6}], fn({x, y}) -> x..y end)
[1, 2, 3, 4, 5, 6]
iex> Enum.flat_map([:a, :b, :c], fn(x) -> [[x]] end)
[[:a], [:b], [:c]]
Maps and reduces an enumerable, flattening the given results (only one level deep).
It expects an accumulator and a function that receives each enumerable
item, and must return a tuple containing a new enumerable (often a list)
with the new accumulator or a tuple with :halt
as first element and
the accumulator as second.
Examples
iex> enum = 1..100
iex> n = 3
iex> Enum.flat_map_reduce(enum, 0, fn i, acc ->
...> if acc < n, do: {[i], acc + 1}, else: {:halt, acc}
...> end)
{[1, 2, 3], 3}
iex> Enum.flat_map_reduce(1..5, 0, fn(i, acc) -> {[[i]], acc + i} end)
{[[1], [2], [3], [4], [5]], 15}
Splits the enumerable into groups based on key_fun
.
The result is a map where each key is given by key_fun
and each
value is a list of elements given by value_fun
. Ordering is preserved.
Examples
iex> Enum.group_by(~w{ant buffalo cat dingo}, &String.length/1)
%{3 => ["ant", "cat"], 7 => ["buffalo"], 5 => ["dingo"]}
iex> Enum.group_by(~w{ant buffalo cat dingo}, &String.length/1, &String.first/1)
%{3 => ["a", "c"], 7 => ["b"], 5 => ["d"]}
Intersperses element
between each element of the enumeration.
Complexity: O(n).
Examples
iex> Enum.intersperse([1, 2, 3], 0)
[1, 0, 2, 0, 3]
iex> Enum.intersperse([1], 0)
[1]
iex> Enum.intersperse([], 0)
[]
into(Enumerable.t, Collectable.t) :: Collectable.t
Inserts the given enumerable
into a collectable
.
Examples
iex> Enum.into([1, 2], [0])
[0, 1, 2]
iex> Enum.into([a: 1, b: 2], %{})
%{a: 1, b: 2}
iex> Enum.into(%{a: 1}, %{b: 2})
%{a: 1, b: 2}
iex> Enum.into([a: 1, a: 2], %{})
%{a: 2}
into(Enumerable.t, Collectable.t, (term -> term)) :: Collectable.t
Inserts the given enumerable
into a collectable
according to the
transformation function.
Examples
iex> Enum.into([2, 3], [3], fn x -> x * 3 end)
[3, 6, 9]
Joins the given enumerable into a binary using joiner
as a
separator.
If joiner
is not passed at all, it defaults to the empty binary.
All items in the enumerable must be convertible to a binary, otherwise an error is raised.
Examples
iex> Enum.join([1, 2, 3])
"123"
iex> Enum.join([1, 2, 3], " = ")
"1 = 2 = 3"
Returns a list where each item is the result of invoking
fun
on each corresponding item of enumerable
.
For maps, the function expects a key-value tuple.
Examples
iex> Enum.map([1, 2, 3], fn(x) -> x * 2 end)
[2, 4, 6]
iex> Enum.map([a: 1, b: 2], fn({k, v}) -> {k, -v} end)
[a: -1, b: -2]
Returns a list of results of invoking fun
on every nth
item of enumerable
, starting with the first element.
The first item is always passed to the given function.
The second argument specifying every nth
item must be a non-negative
integer.
Examples
iex> Enum.map_every(1..10, 2, fn(x) -> x * 2 end)
[2, 2, 6, 4, 10, 6, 14, 8, 18, 10]
iex> Enum.map_every(1..5, 0, fn(x) -> x * 2 end)
[1, 2, 3, 4, 5]
iex> Enum.map_every([1, 2, 3], 1, fn(x) -> x * 2 end)
[2, 4, 6]
Maps and joins the given enumerable in one pass.
joiner
can be either a binary or a list and the result will be of
the same type as joiner
.
If joiner
is not passed at all, it defaults to an empty binary.
All items in the enumerable must be convertible to a binary, otherwise an error is raised.
Examples
iex> Enum.map_join([1, 2, 3], &(&1 * 2))
"246"
iex> Enum.map_join([1, 2, 3], " = ", &(&1 * 2))
"2 = 4 = 6"
Invokes the given function to each item in the enumerable to reduce it to a single element, while keeping an accumulator.
Returns a tuple where the first element is the mapped enumerable and the second one is the final accumulator.
The function, fun
, receives two arguments: the first one is the
element, and the second one is the accumulator. fun
must return
a tuple with two elements in the form of {result, accumulator}
.
For maps, the first tuple element must be a {key, value}
tuple.
Examples
iex> Enum.map_reduce([1, 2, 3], 0, fn(x, acc) -> {x * 2, x + acc} end)
{[2, 4, 6], 6}
Returns the maximal element in the enumerable according to Erlang’s term ordering.
If multiple elements are considered maximal, the first one that was found is returned.
Calls the provided empty_fallback
function and returns its value if
enumerable
is empty. The default empty_fallback
raises Enum.EmptyError
.
Examples
iex> Enum.max([1, 2, 3])
3
iex> Enum.max([], fn -> 0 end)
0
Returns the maximal element in the enumerable as calculated by the given function.
If multiple elements are considered maximal, the first one that was found is returned.
Calls the provided empty_fallback
function and returns its value if
enumerable
is empty. The default empty_fallback
raises Enum.EmptyError
.
Examples
iex> Enum.max_by(["a", "aa", "aaa"], fn(x) -> String.length(x) end)
"aaa"
iex> Enum.max_by(["a", "aa", "aaa", "b", "bbb"], &String.length/1)
"aaa"
iex> Enum.max_by([], &String.length/1, fn -> nil end)
nil
Checks if element
exists within the enumerable.
Membership is tested with the match (===
) operator.
Examples
iex> Enum.member?(1..10, 5)
true
iex> Enum.member?(1..10, 5.0)
false
iex> Enum.member?([1.0, 2.0, 3.0], 2)
false
iex> Enum.member?([1.0, 2.0, 3.0], 2.000)
true
iex> Enum.member?([:a, :b, :c], :d)
false
Returns the minimal element in the enumerable according to Erlang’s term ordering.
If multiple elements are considered minimal, the first one that was found is returned.
Calls the provided empty_fallback
function and returns its value if
enumerable
is empty. The default empty_fallback
raises Enum.EmptyError
.
Examples
iex> Enum.min([1, 2, 3])
1
iex> Enum.min([], fn -> 0 end)
0
Returns the minimal element in the enumerable as calculated by the given function.
If multiple elements are considered minimal, the first one that was found is returned.
Calls the provided empty_fallback
function and returns its value if
enumerable
is empty. The default empty_fallback
raises Enum.EmptyError
.
Examples
iex> Enum.min_by(["a", "aa", "aaa"], fn(x) -> String.length(x) end)
"a"
iex> Enum.min_by(["a", "aa", "aaa", "b", "bbb"], &String.length/1)
"a"
iex> Enum.min_by([], &String.length/1, fn -> nil end)
nil
Returns a tuple with the minimal and the maximal elements in the enumerable according to Erlang’s term ordering.
If multiple elements are considered maximal or minimal, the first one that was found is returned.
Calls the provided empty_fallback
function and returns its value if
enumerable
is empty. The default empty_fallback
raises Enum.EmptyError
.
Examples
iex> Enum.min_max([2, 3, 1])
{1, 3}
iex> Enum.min_max([], fn -> {nil, nil} end)
{nil, nil}
Returns a tuple with the minimal and the maximal elements in the enumerable as calculated by the given function.
If multiple elements are considered maximal or minimal, the first one that was found is returned.
Calls the provided empty_fallback
function and returns its value if
enumerable
is empty. The default empty_fallback
raises Enum.EmptyError
.
Examples
iex> Enum.min_max_by(["aaa", "bb", "c"], fn(x) -> String.length(x) end)
{"c", "aaa"}
iex> Enum.min_max_by(["aaa", "a", "bb", "c", "ccc"], &String.length/1)
{"a", "aaa"}
iex> Enum.min_max_by([], &String.lenth/1, fn -> {nil, nil} end)
{nil, nil}
Returns a random element of an enumerable.
Raises Enum.EmptyError
if enumerable
is empty.
This function uses Erlang’s :rand
module to calculate
the random value. Check its documentation for setting a
different random algorithm or a different seed.
The implementation is based on the
reservoir sampling
algorithm.
It assumes that the sample being returned can fit into memory;
the input enumerable
doesn’t have to, as it is traversed just once.
If a range is passed into the function, this function will pick a random value between the range limits, without traversing the whole range (thus executing in constant time and constant memory).
Examples
# Although not necessary, let's seed the random algorithm
iex> :rand.seed(:exsplus, {101, 102, 103})
iex> Enum.random([1, 2, 3])
2
iex> Enum.random([1, 2, 3])
1
iex> Enum.random(1..1_000)
776
Invokes fun
for each element in the enumerable
, passing that
element and the accumulator as arguments. fun
’s return value
is stored in the accumulator.
The first element of the enumerable is used as the initial value of
the accumulator.
If you wish to use another value for the accumulator, use
Enumerable.reduce/3
.
This function won’t call the specified function for enumerables that
are one-element long.
Returns the accumulator.
Note that since the first element of the enumerable is used as the
initial value of the accumulator, fun
will only be executed n - 1
times where n
is the length of the enumerable.
Examples
iex> Enum.reduce([1, 2, 3, 4], fn(x, acc) -> x * acc end)
24
Invokes fun
for each element in the enumerable
, passing that
element and the accumulator acc
as arguments. fun
’s return value
is stored in acc
.
Returns the accumulator.
Examples
iex> Enum.reduce([1, 2, 3], 0, fn(x, acc) -> x + acc end)
6
Reduces the enumerable until fun
returns {:halt, term}
.
The return value for fun
is expected to be
{:cont, acc}
to continue the reduction withacc
as the new accumulator or{:halt, acc}
to halt the reduction and returnacc
as the return value of this function
Examples
iex> Enum.reduce_while(1..100, 0, fn i, acc ->
...> if i < 3, do: {:cont, acc + i}, else: {:halt, acc}
...> end)
3
Returns elements of enumerable
for which the function fun
returns
false
or nil
.
See also filter/2
.
Examples
iex> Enum.reject([1, 2, 3], fn(x) -> rem(x, 2) == 0 end)
[1, 3]
Returns a list of elements in enumerable
in reverse order.
Examples
iex> Enum.reverse([1, 2, 3])
[3, 2, 1]
Reverses the elements in enumerable
, appends the tail, and returns
it as a list.
This is an optimization for
Enum.concat(Enum.reverse(enumerable), tail)
.
Examples
iex> Enum.reverse([1, 2, 3], [4, 5, 6])
[3, 2, 1, 4, 5, 6]
reverse_slice(t, non_neg_integer, non_neg_integer) :: list
Reverses the enumerable in the range from initial position start
through count
elements.
If count
is greater than the size of the rest of the enumerable,
then this function will reverse the rest of the enumerable.
Examples
iex> Enum.reverse_slice([1, 2, 3, 4, 5, 6], 2, 4)
[1, 2, 6, 5, 4, 3]
Applies the given function to each element in the enumerable, storing the result in a list and passing it as the accumulator for the next computation.
Examples
iex> Enum.scan(1..5, &(&1 + &2))
[1, 3, 6, 10, 15]
Applies the given function to each element in the enumerable,
storing the result in a list and passing it as the accumulator
for the next computation. Uses the given acc
as the starting value.
Examples
iex> Enum.scan(1..5, 0, &(&1 + &2))
[1, 3, 6, 10, 15]
Returns a list with the elements of enumerable
shuffled.
This function uses Erlang’s :rand
module to calculate
the random value. Check its documentation for setting a
different random algorithm or a different seed.
Examples
# Although not necessary, let's seed the random algorithm
iex> :rand.seed(:exsplus, {1, 2, 3})
iex> Enum.shuffle([1, 2, 3])
[2, 1, 3]
iex> Enum.shuffle([1, 2, 3])
[2, 3, 1]
Returns a subset list of the given enumerable, from range.first
to range.last
positions.
Given enumerable
, it drops elements until element position range.first
,
then takes elements until element position range.last
(inclusive).
Positions are normalized, meaning that negative positions will be counted from the end
(e.g. -1
means the last element of the enumerable).
If range.last
is out of bounds, then it is assigned as the position of the last element.
If the normalized range.first
position is out of bounds of the given enumerable,
or this one is greater than the normalized range.last
position, then []
is returned.
Examples
iex> Enum.slice(1..100, 5..10)
[6, 7, 8, 9, 10, 11]
iex> Enum.slice(1..10, 5..20)
[6, 7, 8, 9, 10]
# last five elements (negative positions)
iex> Enum.slice(1..30, -5..-1)
[26, 27, 28, 29, 30]
# last five elements (mixed positive and negative positions)
iex> Enum.slice(1..30, 25..-1)
[26, 27, 28, 29, 30]
# out of bounds
iex> Enum.slice(1..10, 11..20)
[]
# range.first is greater than range.last
iex> Enum.slice(1..10, 6..5)
[]
Returns a subset list of the given enumerable, from start
position with amount
of elements if available.
Given enumerable
, it drops elements until element position start
,
then takes amount
of elements until the end of the enumerable.
If start
is out of bounds, it returns []
.
If amount
is greater than enumerable
length, it returns as many elements as possible.
If amount
is zero, then []
is returned.
Examples
iex> Enum.slice(1..100, 5, 10)
[6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
# amount to take is greater than the number of elements
iex> Enum.slice(1..10, 5, 100)
[6, 7, 8, 9, 10]
iex> Enum.slice(1..10, 5, 0)
[]
# out of bound start position
iex> Enum.slice(1..10, 10, 5)
[]
# out of bound start position (negative)
iex> Enum.slice(1..10, -11, 5)
[]
Sorts the enumerable according to Erlang’s term ordering.
Uses the merge sort algorithm.
Examples
iex> Enum.sort([3, 2, 1])
[1, 2, 3]
Sorts the enumerable by the given function.
This function uses the merge sort algorithm. The given function should compare
two arguments, and return true
if the first argument precedes the second one.
Examples
iex> Enum.sort([1, 2, 3], &(&1 >= &2))
[3, 2, 1]
The sorting algorithm will be stable as long as the given function
returns true
for values considered equal:
iex> Enum.sort ["some", "kind", "of", "monster"], &(byte_size(&1) <= byte_size(&2))
["of", "some", "kind", "monster"]
If the function does not return true
for equal values, the sorting
is not stable and the order of equal terms may be shuffled.
For example:
iex> Enum.sort ["some", "kind", "of", "monster"], &(byte_size(&1) < byte_size(&2))
["of", "kind", "some", "monster"]
Sorts the mapped results of the enumerable according to the provided sorter
function.
This function maps each element of the enumerable using the provided mapper
function. The enumerable is then sorted by the mapped elements
using the sorter
function, which defaults to Kernel.<=/2
sort_by/3
differs from sort/2
in that it only calculates the
comparison value for each element in the enumerable once instead of
once for each element in each comparison.
If the same function is being called on both element, it’s also more
compact to use sort_by/3
.
This technique is also known as a
Schwartzian Transform,
or the Lisp decorate-sort-undecorate idiom as the mapper
is decorating the original enumerable
; then sorter
is sorting the
decorations; and finally the enumerable is being undecorated so only
the original elements remain, but now in sorted order.
Examples
Using the default sorter
of <=/2
:
iex> Enum.sort_by ["some", "kind", "of", "monster"], &byte_size/1
["of", "some", "kind", "monster"]
Using a custom sorter
to override the order:
iex> Enum.sort_by ["some", "kind", "of", "monster"], &byte_size/1, &>=/2
["monster", "some", "kind", "of"]
Splits the enumerable
into two enumerables, leaving count
elements in the first one.
If count
is a negative number, it starts counting from the
back to the beginning of the enumerable.
Be aware that a negative count
implies the enumerable
will be enumerated twice: once to calculate the position, and
a second time to do the actual splitting.
Examples
iex> Enum.split([1, 2, 3], 2)
{[1, 2], [3]}
iex> Enum.split([1, 2, 3], 10)
{[1, 2, 3], []}
iex> Enum.split([1, 2, 3], 0)
{[], [1, 2, 3]}
iex> Enum.split([1, 2, 3], -1)
{[1, 2], [3]}
iex> Enum.split([1, 2, 3], -5)
{[], [1, 2, 3]}
Splits enumerable in two at the position of the element for which
fun
returns false
for the first time.
Examples
iex> Enum.split_while([1, 2, 3, 4], fn(x) -> x < 3 end)
{[1, 2], [3, 4]}
Splits the enumerable
in two lists according to the given function fun
.
Splits the given enumerable
in two lists by calling fun
with each element
in the enumerable
as its only argument. Returns a tuple with the first list
containing all the elements in enumerable
for which applying fun
returned
a truthy value, and a second list with all the elements for which applying
fun
returned a falsey value (false
or nil
).
The elements in both the returned lists are in the same relative order as they were in the original enumerable (if such enumerable was ordered, e.g., a list); see the examples below.
Examples
iex> Enum.split_with([5, 4, 3, 2, 1, 0], fn(x) -> rem(x, 2) == 0 end)
{[4, 2, 0], [5, 3, 1]}
iex> Enum.split_with(%{a: 1, b: -2, c: 1, d: -3}, fn({_k, v}) -> v < 0 end)
{[b: -2, d: -3], [a: 1, c: 1]}
iex> Enum.split_with(%{a: 1, b: -2, c: 1, d: -3}, fn({_k, v}) -> v > 50 end)
{[], [a: 1, b: -2, c: 1, d: -3]}
iex> Enum.split_with(%{}, fn({_k, v}) -> v > 50 end)
{[], []}
Returns the sum of all elements.
Raises ArithmeticError
if enumerable
contains a non-numeric value.
Examples
iex> Enum.sum([1, 2, 3])
6
Takes the first count
items from the enumerable.
count
must be an integer. If a negative count
is given, the last
count
values will be taken.
For such, the enumerable is fully enumerated keeping up
to 2 * count
elements in memory. Once the end of the enumerable is
reached, the last count
elements are returned.
Examples
iex> Enum.take([1, 2, 3], 2)
[1, 2]
iex> Enum.take([1, 2, 3], 10)
[1, 2, 3]
iex> Enum.take([1, 2, 3], 0)
[]
iex> Enum.take([1, 2, 3], -1)
[3]
take_every(t, non_neg_integer) :: list
Returns a list of every nth
item in the enumerable,
starting with the first element.
The first item is always included, unless nth
is 0.
The second argument specifying every nth
item must be a non-negative
integer.
Examples
iex> Enum.take_every(1..10, 2)
[1, 3, 5, 7, 9]
iex> Enum.take_every(1..10, 0)
[]
iex> Enum.take_every([1, 2, 3], 1)
[1, 2, 3]
take_random(t, non_neg_integer) :: list
Takes count
random items from enumerable
.
Notice this function will traverse the whole enumerable
to
get the random sublist.
See random/1
for notes on implementation and random seed.
Examples
# Although not necessary, let's seed the random algorithm
iex> :rand.seed(:exsplus, {1, 2, 3})
iex> Enum.take_random(1..10, 2)
[5, 4]
iex> Enum.take_random(?a..?z, 5)
'ipybz'
Takes the items from the beginning of the enumerable while fun
returns
a truthy value.
Examples
iex> Enum.take_while([1, 2, 3], fn(x) -> x < 3 end)
[1, 2]
Enumerates the enumerable
, removing all duplicated elements.
Examples
iex> Enum.uniq([1, 2, 3, 3, 2, 1])
[1, 2, 3]
Enumerates the enumerable
, by removing the elements for which
function fun
returned duplicate items.
The function fun
maps every element to a term which is used to
determine if two elements are duplicates.
The first occurrence of each element is kept.
Example
iex> Enum.uniq_by([{1, :x}, {2, :y}, {1, :z}], fn {x, _} -> x end)
[{1, :x}, {2, :y}]
iex> Enum.uniq_by([a: {:tea, 2}, b: {:tea, 2}, c: {:coffee, 1}], fn {_, y} -> y end)
[a: {:tea, 2}, c: {:coffee, 1}]
Opposite of Enum.zip/2
; extracts a two-element tuples from the
enumerable and groups them together.
It takes an enumerable with items being two-element tuples and returns a tuple with two lists, each of which is formed by the first and second element of each tuple, respectively.
This function fails unless enumerable
is or can be converted into a
list of tuples with exactly two elements in each tuple.
Examples
iex> Enum.unzip([{:a, 1}, {:b, 2}, {:c, 3}])
{[:a, :b, :c], [1, 2, 3]}
iex> Enum.unzip(%{a: 1, b: 2})
{[:a, :b], [1, 2]}
Returns the enumerable with each element wrapped in a tuple alongside its index.
If an offset
is given, we will index from the given offset instead of from zero.
Examples
iex> Enum.with_index([:a, :b, :c])
[a: 0, b: 1, c: 2]
iex> Enum.with_index([:a, :b, :c], 3)
[a: 3, b: 4, c: 5]
Zips corresponding elements from a collection of enumerables into one list of tuples.
The zipping finishes as soon as any enumerable completes.
Examples
iex> Enum.zip([[1, 2, 3], [:a, :b, :c], ["foo", "bar", "baz"]])
[{1, :a, "foo"}, {2, :b, "bar"}, {3, :c, "baz"}]
iex> Enum.zip([[1, 2, 3, 4, 5], [:a, :b, :c]])
[{1, :a}, {2, :b}, {3, :c}]