Elixir v1.9.2 List View Source
Functions that work on (linked) lists.
Many of the functions provided for lists, which implement
the Enumerable
protocol, are found in the Enum
module.
Additionally, the following functions and operators for lists are
found in Kernel
:
Lists in Elixir are specified between square brackets:
iex> [1, "two", 3, :four]
[1, "two", 3, :four]
Two lists can be concatenated and subtracted using the
Kernel.++/2
and Kernel.--/2
operators:
iex> [1, 2, 3] ++ [4, 5, 6]
[1, 2, 3, 4, 5, 6]
iex> [1, true, 2, false, 3, true] -- [true, false]
[1, 2, 3, true]
Lists in Elixir are effectively linked lists, which means they are internally represented in pairs containing the head and the tail of a list:
iex> [head | tail] = [1, 2, 3]
iex> head
1
iex> tail
[2, 3]
Similarly, we could write the list [1, 2, 3]
using only
such pairs (called cons cells):
iex> [1 | [2 | [3 | []]]]
[1, 2, 3]
Some lists, called improper lists, do not have an empty list as the second element in the last cons cell:
iex> [1 | [2 | [3 | 4]]]
[1, 2, 3 | 4]
Although improper lists are generally avoided, they are used in some
special circumstances like iodata and chardata entities (see the IO
module).
Due to their cons cell based representation, prepending an element to a list is always fast (constant time), while appending becomes slower as the list grows in size (linear time):
iex> list = [1, 2, 3]
iex> [0 | list] # fast
[0, 1, 2, 3]
iex> list ++ [4] # slow
[1, 2, 3, 4]
Most of the functions in this module work in linear time. This means that,
that the time it takes to perform an operation grows at the same rate as the
length of the list. For example length/1
and last/1
will run in linear
time because they need to iterate through every element of the list, but
first/1
will run in constant time because it only needs the first element.
Charlists
If a list is made of non-negative integers, where each integer represents a Unicode code point, the list can also be called a charlist. These integers must:
- be within the range
0..0x10FFFF
(0..1_114_111
); - and be out of the range
0xD800..0xDFFF
(55_296..57_343
), which is reserved in Unicode for UTF-16 surrogate pairs.
Elixir uses single quotes to define charlists:
iex> 'héllo'
[104, 233, 108, 108, 111]
In particular, charlists will be printed back by default in single quotes if they contain only printable ASCII characters:
iex> 'abc'
'abc'
The rationale behind this behaviour is to better support
Erlang libraries which may return text as charlists
instead of Elixir strings. One example of such functions
is Application.loaded_applications/0
:
Application.loaded_applications()
#=> [
#=> {:stdlib, 'ERTS CXC 138 10', '2.6'},
#=> {:compiler, 'ERTS CXC 138 10', '6.0.1'},
#=> {:elixir, 'elixir', '1.0.0'},
#=> {:kernel, 'ERTS CXC 138 10', '4.1'},
#=> {:logger, 'logger', '1.0.0'}
#=> ]
A list can be checked if it is made of only printable ASCII
characters with ascii_printable?/2
.
Improper lists are never deemed as charlists.
Link to this section Summary
Functions
Checks if list
is a charlist made only of printable ASCII characters.
Deletes the given element
from the list
. Returns a new list without
the element.
Produces a new list by removing the value at the specified index
.
Duplicates the given element n
times in a list.
Returns the first element in list
or nil
if list
is empty.
Flattens the given list
of nested lists.
Flattens the given list
of nested lists.
The list tail
will be added at the end of
the flattened list.
Folds (reduces) the given list from the left with a function. Requires an accumulator.
Folds (reduces) the given list from the right with a function. Requires an accumulator.
Returns true
if list
is an improper list. Otherwise returns false
.
Returns a list with value
inserted at the specified index
.
Receives a list
of tuples and deletes the first tuple
where the element at position
matches the
given key
. Returns the new list.
Receives a list of tuples and returns the first tuple
where the element at position
in the tuple matches the
given key
.
Receives a list of tuples and returns true
if there is
a tuple where the element at position
in the tuple matches
the given key
.
Receives a list of tuples and if the identified element by key
at position
exists, it is replaced with new_tuple
.
Receives a list of tuples and sorts the elements
at position
of the tuples. The sort is stable.
Receives a list
of tuples and replaces the element
identified by key
at position
with new_tuple
.
Receives a list
of tuples and returns the first tuple
where the element at position
in the tuple matches the
given key
, as well as the list
without found tuple.
Returns the last element in list
or nil
if list
is empty.
Returns a keyword list that represents an edit script.
Returns a keyword list that represents an edit script with nested diffs.
Returns and removes the value at the specified index
in the list
.
Returns a list with a replaced value at the specified index
.
Returns true
if list
starts with the given prefix
list; otherwise returns false
.
Converts a charlist to an atom.
Converts a list of integers representing code points, lists or strings into a charlist.
Converts a charlist to an existing atom. Raises an ArgumentError
if the atom does not exist.
Returns the float whose text representation is charlist
.
Returns an integer whose text representation is charlist
.
Returns an integer whose text representation is charlist
in base base
.
Converts a list of integers representing code points, lists or strings into a string.
Converts a list to a tuple.
Returns a list with an updated value at the specified index
.
Wraps term
in a list if this is not list.
Zips corresponding elements from each list in list_of_lists
.
Link to this section Functions
Specs
ascii_printable?(list(), 0) :: true
ascii_printable?([], limit) :: true when limit: :infinity | pos_integer()
ascii_printable?([...], limit) :: boolean() when limit: :infinity | pos_integer()
Checks if list
is a charlist made only of printable ASCII characters.
Takes an optional limit
as a second argument. ascii_printable?/2
only
checks the printability of the list up to the limit
.
A printable charlist in Elixir contains only the printable characters in the standard seven-bit ASCII character encoding, which are characters ranging from 32 to 126 in decimal notation, plus the following control characters:
?\a
- Bell?\b
- Backspace?\t
- Horizontal tab?\n
- Line feed?\v
- Vertical tab?\f
- Form feed?\r
- Carriage return?\e
- Escape
For more information read the Character groups section in the Wikipedia article of the ASCII standard.
Examples
iex> List.ascii_printable?('abc')
true
iex> List.ascii_printable?('abc' ++ [0])
false
iex> List.ascii_printable?('abc' ++ [0], 2)
true
Improper lists are not printable, even if made only of ASCII characters:
iex> List.ascii_printable?('abc' ++ ?d)
false
Specs
Deletes the given element
from the list
. Returns a new list without
the element.
If the element
occurs more than once in the list
, just
the first occurrence is removed.
Examples
iex> List.delete([:a, :b, :c], :a)
[:b, :c]
iex> List.delete([:a, :b, :c], :d)
[:a, :b, :c]
iex> List.delete([:a, :b, :b, :c], :b)
[:a, :b, :c]
iex> List.delete([], :b)
[]
Specs
Produces a new list by removing the value at the specified index
.
Negative indices indicate an offset from the end of the list
.
If index
is out of bounds, the original list
is returned.
Examples
iex> List.delete_at([1, 2, 3], 0)
[2, 3]
iex> List.delete_at([1, 2, 3], 10)
[1, 2, 3]
iex> List.delete_at([1, 2, 3], -1)
[1, 2]
Specs
duplicate(any(), 0) :: []
duplicate(elem, pos_integer()) :: [elem, ...] when elem: var
Duplicates the given element n
times in a list.
n
is an integer greater than or equal to 0
.
If n
is 0
, an empty list is returned.
Examples
iex> List.duplicate("hello", 0)
[]
iex> List.duplicate("hi", 1)
["hi"]
iex> List.duplicate("bye", 2)
["bye", "bye"]
iex> List.duplicate([1, 2], 3)
[[1, 2], [1, 2], [1, 2]]
Specs
first([]) :: nil
first([elem, ...]) :: elem when elem: var
Returns the first element in list
or nil
if list
is empty.
Examples
iex> List.first([])
nil
iex> List.first([1])
1
iex> List.first([1, 2, 3])
1
Specs
Flattens the given list
of nested lists.
Empty list elements are discarded.
Examples
iex> List.flatten([1, [[2], 3]])
[1, 2, 3]
iex> List.flatten([[], [[], []]])
[]
Specs
flatten(deep_list, [elem]) :: [elem] when deep_list: [elem | deep_list], elem: var
Flattens the given list
of nested lists.
The list tail
will be added at the end of
the flattened list.
Empty list elements from list
are discarded,
but not the ones from tail
.
Examples
iex> List.flatten([1, [[2], 3]], [4, 5])
[1, 2, 3, 4, 5]
iex> List.flatten([1, [], 2], [3, [], 4])
[1, 2, 3, [], 4]
Specs
foldl([elem], acc, (elem, acc -> acc)) :: acc when elem: var, acc: var
Folds (reduces) the given list from the left with a function. Requires an accumulator.
Examples
iex> List.foldl([5, 5], 10, fn x, acc -> x + acc end)
20
iex> List.foldl([1, 2, 3, 4], 0, fn x, acc -> x - acc end)
2
Specs
foldr([elem], acc, (elem, acc -> acc)) :: acc when elem: var, acc: var
Folds (reduces) the given list from the right with a function. Requires an accumulator.
Examples
iex> List.foldr([1, 2, 3, 4], 0, fn x, acc -> x - acc end)
-2
Specs
improper?(maybe_improper_list()) :: boolean()
Returns true
if list
is an improper list. Otherwise returns false
.
Examples
iex> List.improper?([1, 2 | 3])
true
iex> List.improper?([1, 2, 3])
false
Specs
Returns a list with value
inserted at the specified index
.
Note that index
is capped at the list length. Negative indices
indicate an offset from the end of the list
.
Examples
iex> List.insert_at([1, 2, 3, 4], 2, 0)
[1, 2, 0, 3, 4]
iex> List.insert_at([1, 2, 3], 10, 0)
[1, 2, 3, 0]
iex> List.insert_at([1, 2, 3], -1, 0)
[1, 2, 3, 0]
iex> List.insert_at([1, 2, 3], -10, 0)
[0, 1, 2, 3]
Specs
keydelete([tuple()], any(), non_neg_integer()) :: [tuple()]
Receives a list
of tuples and deletes the first tuple
where the element at position
matches the
given key
. Returns the new list.
Examples
iex> List.keydelete([a: 1, b: 2], :a, 0)
[b: 2]
iex> List.keydelete([a: 1, b: 2], 2, 1)
[a: 1]
iex> List.keydelete([a: 1, b: 2], :c, 0)
[a: 1, b: 2]
Specs
keyfind([tuple()], any(), non_neg_integer(), any()) :: any()
Receives a list of tuples and returns the first tuple
where the element at position
in the tuple matches the
given key
.
If no matching tuple is found, default
is returned.
Examples
iex> List.keyfind([a: 1, b: 2], :a, 0)
{:a, 1}
iex> List.keyfind([a: 1, b: 2], 2, 1)
{:b, 2}
iex> List.keyfind([a: 1, b: 2], :c, 0)
nil
Specs
keymember?([tuple()], any(), non_neg_integer()) :: boolean()
Receives a list of tuples and returns true
if there is
a tuple where the element at position
in the tuple matches
the given key
.
Examples
iex> List.keymember?([a: 1, b: 2], :a, 0)
true
iex> List.keymember?([a: 1, b: 2], 2, 1)
true
iex> List.keymember?([a: 1, b: 2], :c, 0)
false
Specs
keyreplace([tuple()], any(), non_neg_integer(), tuple()) :: [tuple()]
Receives a list of tuples and if the identified element by key
at position
exists, it is replaced with new_tuple
.
Examples
iex> List.keyreplace([a: 1, b: 2], :a, 0, {:a, 3})
[a: 3, b: 2]
iex> List.keyreplace([a: 1, b: 2], :a, 1, {:a, 3})
[a: 1, b: 2]
Specs
keysort([tuple()], non_neg_integer()) :: [tuple()]
Receives a list of tuples and sorts the elements
at position
of the tuples. The sort is stable.
Examples
iex> List.keysort([a: 5, b: 1, c: 3], 1)
[b: 1, c: 3, a: 5]
iex> List.keysort([a: 5, c: 1, b: 3], 0)
[a: 5, b: 3, c: 1]
Specs
keystore([tuple()], any(), non_neg_integer(), tuple()) :: [tuple(), ...]
Receives a list
of tuples and replaces the element
identified by key
at position
with new_tuple
.
If the element does not exist, it is added to the end of the list
.
Examples
iex> List.keystore([a: 1, b: 2], :a, 0, {:a, 3})
[a: 3, b: 2]
iex> List.keystore([a: 1, b: 2], :c, 0, {:c, 3})
[a: 1, b: 2, c: 3]
Specs
keytake([tuple()], any(), non_neg_integer()) :: {tuple(), [tuple()]} | nil
Receives a list
of tuples and returns the first tuple
where the element at position
in the tuple matches the
given key
, as well as the list
without found tuple.
If such a tuple is not found, nil
will be returned.
Examples
iex> List.keytake([a: 1, b: 2], :a, 0)
{{:a, 1}, [b: 2]}
iex> List.keytake([a: 1, b: 2], 2, 1)
{{:b, 2}, [a: 1]}
iex> List.keytake([a: 1, b: 2], :c, 0)
nil
Specs
last([]) :: nil
last([elem, ...]) :: elem when elem: var
Returns the last element in list
or nil
if list
is empty.
Examples
iex> List.last([])
nil
iex> List.last([1])
1
iex> List.last([1, 2, 3])
3
Specs
Returns a keyword list that represents an edit script.
The algorithm is outlined in the "An O(ND) Difference Algorithm and Its Variations" paper by E. Myers.
An edit script is a keyword list. Each key describes the "editing action" to
take in order to bring list1
closer to being equal to list2
; a key can be
:eq
, :ins
, or :del
. Each value is a sublist of either list1
or list2
that should be inserted (if the corresponding key :ins
), deleted (if the
corresponding key is :del
), or left alone (if the corresponding key is
:eq
) in list1
in order to be closer to list2
.
See myers_difference/3
if you want to handle nesting in the diff scripts.
Examples
iex> List.myers_difference([1, 4, 2, 3], [1, 2, 3, 4])
[eq: [1], del: [4], eq: [2, 3], ins: [4]]
Specs
myers_difference(list(), list(), (term(), term() -> script | nil)) :: script when script: [{:eq | :ins | :del | :diff, list()}]
Returns a keyword list that represents an edit script with nested diffs.
This is an extension of myers_difference/2
where a diff_script
function
can be given in case it is desired to compute nested differences. The function
may return a list with the inner edit script or nil
in case there is no
such script. The returned inner edit script will be under the :diff
key.
Examples
iex> List.myers_difference(["a", "db", "c"], ["a", "bc"], &String.myers_difference/2)
[eq: ["a"], diff: [del: "d", eq: "b", ins: "c"], del: ["c"]]
Specs
Returns and removes the value at the specified index
in the list
.
Negative indices indicate an offset from the end of the list
.
If index
is out of bounds, the original list
is returned.
Examples
iex> List.pop_at([1, 2, 3], 0)
{1, [2, 3]}
iex> List.pop_at([1, 2, 3], 5)
{nil, [1, 2, 3]}
iex> List.pop_at([1, 2, 3], 5, 10)
{10, [1, 2, 3]}
iex> List.pop_at([1, 2, 3], -1)
{3, [1, 2]}
Specs
Returns a list with a replaced value at the specified index
.
Negative indices indicate an offset from the end of the list
.
If index
is out of bounds, the original list
is returned.
Examples
iex> List.replace_at([1, 2, 3], 0, 0)
[0, 2, 3]
iex> List.replace_at([1, 2, 3], 10, 0)
[1, 2, 3]
iex> List.replace_at([1, 2, 3], -1, 0)
[1, 2, 0]
iex> List.replace_at([1, 2, 3], -10, 0)
[1, 2, 3]
Specs
starts_with?([...], [...]) :: boolean()
starts_with?(list(), []) :: true
starts_with?([], [...]) :: false
Returns true
if list
starts with the given prefix
list; otherwise returns false
.
If prefix
is an empty list, it returns true
.
Examples
iex> List.starts_with?([1, 2, 3], [1, 2])
true
iex> List.starts_with?([1, 2], [1, 2, 3])
false
iex> List.starts_with?([:alpha], [])
true
iex> List.starts_with?([], [:alpha])
false
Specs
Converts a charlist to an atom.
Elixir supports conversions from charlists which contains any Unicode code point.
Inlined by the compiler.
Examples
iex> List.to_atom('Elixir')
:Elixir
iex> List.to_atom('🌢 Elixir')
:"🌢 Elixir"
Specs
to_charlist(:unicode.charlist()) :: charlist()
Converts a list of integers representing code points, lists or strings into a charlist.
Notice that this function expects a list of integers representing
UTF-8 code points. If you have a list of bytes, you must instead use
the :binary
module.
Examples
iex> List.to_charlist([0x00E6, 0x00DF])
'æß'
iex> List.to_charlist([0x0061, "bc"])
'abc'
iex> List.to_charlist([0x0064, "ee", ['p']])
'deep'
Specs
Converts a charlist to an existing atom. Raises an ArgumentError
if the atom does not exist.
Elixir supports conversions from charlists which contains any Unicode code point.
Inlined by the compiler.
Examples
iex> _ = :my_atom
iex> List.to_existing_atom('my_atom')
:my_atom
iex> _ = :"🌢 Elixir"
iex> List.to_existing_atom('🌢 Elixir')
:"🌢 Elixir"
iex> List.to_existing_atom('this_atom_will_never_exist')
** (ArgumentError) argument error
Specs
Returns the float whose text representation is charlist
.
Inlined by the compiler.
Examples
iex> List.to_float('2.2017764e+0')
2.2017764
Specs
Returns an integer whose text representation is charlist
.
Inlined by the compiler.
Examples
iex> List.to_integer('123')
123
Specs
Returns an integer whose text representation is charlist
in base base
.
Inlined by the compiler.
Examples
iex> List.to_integer('3FF', 16)
1023
Specs
to_string(:unicode.charlist()) :: String.t()
Converts a list of integers representing code points, lists or strings into a string.
To be converted to a string, a list must either be empty or only contain the following elements:
- strings
- integers representing Unicode code points
- a list containing one of these three elements
Notice that this function expects a list of integers representing
UTF-8 code points. If you have a list of bytes, you must instead use
the :binary
module.
Examples
iex> List.to_string([0x00E6, 0x00DF])
"æß"
iex> List.to_string([0x0061, "bc"])
"abc"
iex> List.to_string([0x0064, "ee", ['p']])
"deep"
iex> List.to_string([])
""
Specs
Converts a list to a tuple.
Inlined by the compiler.
Examples
iex> List.to_tuple([:share, [:elixir, 163]])
{:share, [:elixir, 163]}
Specs
Returns a list with an updated value at the specified index
.
Negative indices indicate an offset from the end of the list
.
If index
is out of bounds, the original list
is returned.
Examples
iex> List.update_at([1, 2, 3], 0, &(&1 + 10))
[11, 2, 3]
iex> List.update_at([1, 2, 3], 10, &(&1 + 10))
[1, 2, 3]
iex> List.update_at([1, 2, 3], -1, &(&1 + 10))
[1, 2, 13]
iex> List.update_at([1, 2, 3], -10, &(&1 + 10))
[1, 2, 3]
Specs
wrap(term()) :: maybe_improper_list()
Wraps term
in a list if this is not list.
If term
is already a list, it returns the list.
If term
is nil
, it returns an empty list.
Examples
iex> List.wrap("hello")
["hello"]
iex> List.wrap([1, 2, 3])
[1, 2, 3]
iex> List.wrap(nil)
[]
Specs
Zips corresponding elements from each list in list_of_lists
.
The zipping finishes as soon as any list terminates.
Examples
iex> List.zip([[1, 2], [3, 4], [5, 6]])
[{1, 3, 5}, {2, 4, 6}]
iex> List.zip([[1, 2], [3], [5, 6]])
[{1, 3, 5}]