Elixir v1.4.2 List View Source
Functions that work on (linked) lists.
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]The Kernel module contains many functions to manipulate lists
and that are allowed in guards. For example, Kernel.hd/1 to
retrieve the head, Kernel.tl/1 to fetch the tail and
Kernel.length/1 for calculating the length. Keep in mind that,
similar to appending to a list, calculating the length needs to
traverse the whole list.
Charlists
If a list is made of non-negative integers, it can also be called a charlist. Elixir uses single quotes to define charlists:
iex> 'héllo'
[104, 233, 108, 108, 111]In particular, charlists may be printed back in single quotes if they contain only ASCII-printable codepoints:
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'}]List and Enum modules
This module aims to provide operations that are specific
to lists, like conversion between data types, updates,
deletions and key lookups (for lists of tuples). For traversing
lists in general, developers should use the functions in the
Enum module that work across a variety of data types.
In both Enum and List modules, any kind of index access
on a list is linear. Negative indexes are also supported but
they imply the list will be iterated twice, one to calculate
the proper index and another to perform the operation.
Link to this section Summary
Functions
Deletes the given item from the list. Returns a new list without
the item
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 a list with value inserted at the specified index
Receives a list of tuples and deletes the first tuple
where the item at position matches the
given key. Returns the new list
Receives a list of tuples and returns the first tuple
where the item at position in the tuple matches the
given key
Receives a list of tuples and returns true if there is
a tuple where the item at position in the tuple matches
the given key
Receives a list of tuples and replaces the item
identified by key at position if it exists
Receives a list of tuples and sorts the items
at position of the tuples. The sort is stable
Receives a list of tuples and replaces the item
identified by key at position
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 and removes the value at the specified index in the list
Returns a list with a replaced value at the specified index
Converts a charlist to an atom
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 codepoints, lists or strings into a string
Converts a list to a tuple
Returns a list with an updated value at the specified index
Wraps the argument in a list
Zips corresponding elements from each list in list_of_lists
Link to this section Functions
Deletes the given item from the list. Returns a new list without
the item.
If the item 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, :b, :c], :b)
[:a, :b, :c]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]duplicate(elem, non_neg_integer) :: [elem] when elem: var
Duplicates the given element n times in a list.
Examples
iex> List.duplicate("hello", 3)
["hello", "hello", "hello"]
iex> List.duplicate([1, 2], 2)
[[1, 2], [1, 2]]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])
1flatten(deep_list) :: list when deep_list: [any | deep_list]
Flattens the given list of nested lists.
Examples
iex> List.flatten([1, [[2], 3]])
[1, 2, 3]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.
Examples
iex> List.flatten([1, [[2], 3]], [4, 5])
[1, 2, 3, 4, 5]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)
2foldr([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)
-2insert_at(list, integer, any) :: list
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]keydelete([tuple], any, non_neg_integer) :: [tuple]
Receives a list of tuples and deletes the first tuple
where the item 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]keyfind([tuple], any, non_neg_integer, any) :: any
Receives a list of tuples and returns the first tuple
where the item at position in the tuple matches the
given key.
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)
nilkeymember?([tuple], any, non_neg_integer) :: boolean
Receives a list of tuples and returns true if there is
a tuple where the item 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)
falsekeyreplace([tuple], any, non_neg_integer, tuple) :: [tuple]
Receives a list of tuples and replaces the item
identified by key at position if it exists.
Examples
iex> List.keyreplace([a: 1, b: 2], :a, 0, {:a, 3})
[a: 3, b: 2]keysort([tuple], non_neg_integer) :: [tuple]
Receives a list of tuples and sorts the items
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]keystore([tuple], any, non_neg_integer, tuple) :: [tuple, ...]
Receives a list of tuples and replaces the item
identified by key at position.
If the item 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]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)
nilReturns 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])
3myers_difference(list, list) ::
[{:eq | :ins | :del, list}] |
nil
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.
Examples
iex> List.myers_difference([1, 4, 2, 3], [1, 2, 3, 4])
[eq: [1], del: [4], eq: [2, 3], ins: [4]]pop_at(list, integer, any) :: {any, list}
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]}replace_at(list, integer, any) :: list
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]Converts a charlist to an atom.
Currently Elixir does not support conversions from charlists which contains Unicode codepoints greater than 0xFF.
Inlined by the compiler.
Examples
iex> List.to_atom('elixir')
:elixirConverts a charlist to an existing atom. Raises an ArgumentError
if the atom does not exist.
Currently Elixir does not support conversions from charlists which contains Unicode codepoints greater than 0xFF.
Inlined by the compiler.
Examples
iex> _ = :my_atom
iex> List.to_existing_atom('my_atom')
:my_atom
iex> List.to_existing_atom('this_atom_will_never_exist')
** (ArgumentError) argument errorReturns the float whose text representation is charlist.
Inlined by the compiler.
Examples
iex> List.to_float('2.2017764e+0')
2.2017764Returns an integer whose text representation is charlist.
Inlined by the compiler.
Examples
iex> List.to_integer('123')
123Returns an integer whose text representation is charlist in base base.
Inlined by the compiler.
Examples
iex> List.to_integer('3FF', 16)
1023Converts a list of integers representing codepoints, lists or strings into a string.
Notice that this function expects a list of integers representing
UTF-8 codepoints. 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"Converts a list to a tuple.
Inlined by the compiler.
Examples
iex> List.to_tuple([:share, [:elixir, 163]])
{:share, [:elixir, 163]}update_at([elem], integer, (elem -> any)) :: list when elem: var
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]Wraps the argument in a list.
If the argument is already a list, returns the list.
If the argument is nil, returns an empty list.
Examples
iex> List.wrap("hello")
["hello"]
iex> List.wrap([1, 2, 3])
[1, 2, 3]
iex> List.wrap(nil)
[]