Shortcut to chunk(enumerable, count, count).

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 size of the enumerable.

Examples

iex> Enum.count([1, 2, 3])
3

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 ===.

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 first n items from then enumerable.

If a negative value n is given, the last n 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]

Drops items at the beginning of the enumerable while fun returns a truthy value.

Examples

iex> Enum.drop_while([1, 2, 3, 4, 5], fn(x) -> x < 3 end)
[3, 4, 5]

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], 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.

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]

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

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]

Maps and reduces an enumerable, flattening the given results.

It expects an accumulator and a function that receives each stream item, and must return a tuple containing a new stream (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}

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)
[]

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}

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]

Returns a list where each item is the result of invoking fun on each corresponding item of enumerable.

For dicts, 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]

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 a tuple with two elements in the form of {result, accumulator}.

For dicts, 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 biggest of the elements in the enumerable according to Erlang’s term ordering.

If more than one elements compare equal, the first one that was found is returned.

Raises Enum.EmptyError if enumerable is empty.

Examples

iex> Enum.max([1, 2, 3])
3

Returns the biggest of the elements in the enumerable as calculated by the given function.

If more than one elements compare equal, the first one that was found is returned.

Raises Enum.EmptyError if enumerable is empty.

Examples

iex> Enum.max_by(["a", "aa", "aaa"], fn(x) -> String.length(x) end)
"aaa"

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 smallest of the elements in the enumerable according to Erlang’s term ordering.

If more than one elements compare equal, the first one that was found is returned.

Raises Enum.EmptyError if enumerable is empty.

Examples

iex> Enum.min([1, 2, 3])
1

Returns the smallest of the elements in the enumerable as calculated by the given function.

If more than one elements compare equal, the first one that was found is returned.

Raises Enum.EmptyError if enumerable is empty.

Examples

iex> Enum.min_by(["a", "aa", "aaa"], fn(x) -> String.length(x) end)
"a"

Returns a tuple with the smallest and the biggest elements in the enumerable according to Erlang’s term ordering.

If more than one elements compare equal, the first one that was found is picked.

Raises Enum.EmptyError if enumerable is empty.

Examples

iex> Enum.min_max([2, 3, 1])
{1, 3}

Returns a tuple with the smallest and the biggest elements in the enumerable as calculated by the given function.

If more than one elements compare equal, the first one that was found is picked.

Raises Enum.EmptyError if enumerable is empty.

Examples

iex> Enum.min_max_by(["aaa", "bb", "c"], fn(x) -> String.length(x) end)
{"c", "aaa"}

Partitions enumerable into two enumerables, where the first one contains elements for which fun returns a truthy value, and the second one – for which fun returns false or nil.

Examples

iex> Enum.partition([1, 2, 3], fn(x) -> rem(x, 2) == 0 end)
{[2], [1, 3]}

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.

Examples

# Although not necessary, let's seed the random algorithm
iex> :rand.seed(:exsplus, {1, 2, 3})
iex> Enum.random([1, 2, 3])
2
iex> Enum.random([1, 2, 3])
1

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 1-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 halt is emitted.

The return value for fun is expected to be {:cont, acc}, return {:halt, acc} to end the reduction early.

Returns the accumulator.

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.

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]

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. Drops elements until element position range.first, then takes elements until element position range.last (inclusive).

Positions are calculated by adding the number of items in the enumerable to negative positions (e.g. position -3 in an enumerable with count 5 becomes position 2).

The first position (after adding count to negative positions) must be smaller or equal to the last position.

If the start of the range is not a valid offset for the given enumerable or if the range is in reverse order, returns [].

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]

iex> Enum.slice(1..10, 11..20)
[]

iex> Enum.slice(1..10, 6..5)
[]

Returns a subset list of the given enumerable. Drops elements until element position start, then takes count elements.

If the count is greater than enumerable length, it returns as many as possible. If zero, then it returns [].

Examples

iex> Enum.slice(1..100, 5, 10)
[6, 7, 8, 9, 10, 11, 12, 13, 14, 15]

iex> Enum.slice(1..10, 5, 100)
[6, 7, 8, 9, 10]

iex> Enum.slice(1..10, 5, 0)
[]

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 must return false if the first argument is smaller than 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"]

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]}

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]

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, otherwise FunctionClauseError will be raised.

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]

Takes random items from the enumerable.

Notice this function will traverse the whole enumerable to get the random sublist of enumerable. If you want the random number between two integers, the best option is to use the :random module.

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, 8]
iex> Enum.take_random(?a..?z, 5)
'fhjni'

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]

Converts enumerable to a list.

Examples

iex> Enum.to_list(1..3)
[1, 2, 3]

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.

Example

iex> Enum.uniq_by([{1, :x}, {2, :y}, {1, :z}], fn {x, _} -> x end)
[{1, :x}, {2, :y}]

Enum.uniq_by([{a: {tea: 2}}, {b: {tea: 2}}, {c, {coffe: 1}}], fn {x, _} -> x end)
[a: [tea: 2], b: [tea: 2]]

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]}

Zips corresponding elements from two 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])
[{1, :a}, {2, :b}, {3, :c}]

iex> Enum.zip([1, 2, 3, 4, 5], [:a, :b, :c])
[{1, :a}, {2, :b}, {3, :c}]