lists
List Processing Functions
This module contains functions for list processing. The functions are organized in two groups: those in the first group perform a particular operation on one or more lists, whereas those in the second group are higher-order functions, using a fun as argument to perform an operation on one list.
Unless otherwise stated, all functions assume that position numbering starts at 1. That is, the first element of a list is at position 1.
Whenever an ordering function
F
is expected as argument, it is assumed that the
following properties hold of F
for all x, y and z:
if x
F
y and yF
x then x = y (F
is antisymmetric);if x
F
y and and yF
z then xF
z (F
is transitive);x
F
y or yF
x (F
is total).
An example of a typical ordering function is less than or equal
to, =</2
.
Functions
all(Pred, List) -> bool()
Pred = fun(Elem) -> bool()
Elem = term()
List = [term()]
Returns true
if Pred(Elem)
returns
true
for all elements Elem
in List
,
otherwise false
.
any(Pred, List) -> bool()
Pred = fun(Elem) -> bool()
Elem = term()
List = [term()]
Returns true
if Pred(Elem)
returns
true
for at least one element Elem
in
List
.
append(ListOfLists) -> List1
ListOfLists = [List]
List = List1 = [term()]
Returns a list in which all the sub-lists of
ListOfLists
have been appended. For example:
> lists:append([[1, 2, 3], [a, b], [4, 5, 6]]).
[1,2,3,a,b,4,5,6]
append(List1, List2) -> List3
List1 = List2 = List3 = [term()]
Returns a new list List3
which is made from
the elements of List1
followed by the elements of
List2
. For example:
> lists:append("abc", "def").
"abcdef"
lists:append(A, B)
is equivalent to A ++ B
.
concat(Things) -> string()
Things = [Thing]
Thing = atom() | integer() | float() | string()
Concatenates the text representation of the elements
of Things
. The elements of Things
can be atoms,
integers, floats or strings.
> lists:concat([doc, '/', file, '.', 3]).
"doc/file.3"
delete(Elem, List1) -> List2
Elem = term()
List1 = List2 = [term()]
Returns a copy of List1
where the first element
matching Elem
is deleted, if there is such an
element.
dropwhile(Pred, List1) -> List2
Pred = fun(Elem) -> bool()
Elem = term()
List1 = List2 = [term()]
Drops elements Elem
from List1
while
Pred(Elem)
returns true
and returns
the remaining list.
duplicate(N, Elem) -> List
N = int()
Elem = term()
List = [term()]
Returns a list which contains N copies of the term
Elem
. For example:
> lists:duplicate(5, xx).
[xx,xx,xx,xx,xx]
filter(Pred, List1) -> List2
Pred = fun(Elem) -> bool()
Elem = term()
List1 = List2 = [term()]
List2
is a list of all elements Elem
in
List1
for which Pred(Elem)
returns
true
.
flatlength(DeepList) -> int()
DeepList = [term() | DeepList]
Equivalent to length(flatten(DeepList))
, but more
efficient.
flatmap(Fun, List1) -> List2
Fun = fun(A) -> [B]
List1 = [A]
List2 = [B]
A = B = term()
Takes a function from A
s to lists of B
s, and a
list of A
s (List1
) and produces a list of
B
s by applying the function to every element in
List1
and appending the resulting lists.
That is, flatmap
behaves as if it had been defined as
follows:
flatmap(Fun, List1) -> append(map(Fun, List1))
Example:
> lists:flatmap(fun(X)->[X,X] end, [a,b,c]).
[a,a,b,b,c,c]
flatten(DeepList) -> List
DeepList = [term() | DeepList]
List = [term()]
Returns a flattened version of DeepList
.
flatten(DeepList, Tail) -> List
DeepList = [term() | DeepList]
Tail = List = [term()]
Returns a flattened version of DeepList
with the tail
Tail
appended.
foldl(Fun, Acc0, List) -> Acc1
Fun = fun(Elem, AccIn) -> AccOut
Elem = term()
Acc0 = Acc1 = AccIn = AccOut = term()
List = [term()]
Calls Fun(Elem, AccIn)
on successive elements A
of List
, starting with AccIn == Acc0
.
Fun/2
must return a new accumulator which is passed to
the next call. The function returns the final value of
the accumulator. Acc0
is returned if the list is empty.
For example:
>lists:foldl(fun(X, Sum) -> X + Sum end, 0, [1,2,3,4,5]).
15 >lists:foldl(fun(X, Prod) -> X * Prod end, 1, [1,2,3,4,5]).
120
foldr(Fun, Acc0, List) -> Acc1
Fun = fun(Elem, AccIn) -> AccOut
Elem = term()
Acc0 = Acc1 = AccIn = AccOut = term()
List = [term()]
Like foldl/3
, but the list is traversed from right to
left. For example:
>P = fun(A, AccIn) -> io:format("~p ", [A]), AccIn end.
#Fun<erl_eval.12.2225172> >lists:foldl(P, void, [1,2,3]).
1 2 3 void >lists:foldr(P, void, [1,2,3]).
3 2 1 void
foldl/3
is tail recursive and would usually be
preferred to foldr/3
.
foreach(Fun, List) -> void()
Fun = fun(Elem) -> void()
Elem = term()
List = [term()]
Calls Fun(Elem)
for each element Elem
in
List
. This function is used for its side effects and
the evaluation order is defined to be the same as the order
of the elements in the list.
keydelete(Key, N, TupleList1) -> TupleList2
Key = term()
N = 1..tuple_size(Tuple)
TupleList1 = TupleList2 = [Tuple]
Tuple = tuple()
Returns a copy of TupleList1
where the first
occurrence of a tuple whose N
th element compares equal to
Key
is deleted, if there is such a tuple.
keyfind(Key, N, TupleList) -> Tuple | false
Key = term()
N = 1..tuple_size(Tuple)
TupleList = [Tuple]
Tuple = tuple()
Searches the list of tuples TupleList
for a
tuple whose N
th element compares equal to Key
.
Returns Tuple
if such a tuple is found,
otherwise false
.
keymap(Fun, N, TupleList1) -> TupleList2
Fun = fun(Term1) -> Term2
Term1 = Term2 = term()
N = 1..tuple_size(Tuple)
TupleList1 = TupleList2 = [tuple()]
Returns a list of tuples where, for each tuple in
TupleList1
, the N
th element Term1
of the tuple
has been replaced with the result of calling
Fun(Term1)
.
Examples:
>Fun = fun(Atom) -> atom_to_list(Atom) end.
#Fun<erl_eval.6.10732646> 2>lists:keymap(Fun, 2, [{name,jane,22},{name,lizzie,20},{name,lydia,15}]).
[{name,"jane",22},{name,"lizzie",20},{name,"lydia",15}]
keymember(Key, N, TupleList) -> bool()
Key = term()
N = 1..tuple_size(Tuple)
TupleList = [Tuple]
Tuple = tuple()
Returns true
if there is a tuple in TupleList
whose N
th element compares equal to Key
, otherwise
false
.
keymerge(N, TupleList1, TupleList2) -> TupleList3
N = 1..tuple_size(Tuple)
TupleList1 = TupleList2 = TupleList3 = [Tuple]
Tuple = tuple()
Returns the sorted list formed by merging TupleList1
and TupleList2
. The merge is performed on
the N
th element of each tuple. Both TupleList1
and
TupleList2
must be key-sorted prior to evaluating this
function. When two tuples compare equal, the tuple from
TupleList1
is picked before the tuple from
TupleList2
.
keyreplace(Key, N, TupleList1, NewTuple) -> TupleList2
Key = term()
N = 1..tuple_size(Tuple)
TupleList1 = TupleList2 = [Tuple]
NewTuple = Tuple = tuple()
Returns a copy of TupleList1
where the first
occurrence of a T
tuple whose N
th element
compares equal to Key
is replaced with
NewTuple
, if there is such a tuple T
.
keysearch(Key, N, TupleList) -> {value, Tuple} | false
Key = term()
N = 1..tuple_size(Tuple)
TupleList = [Tuple]
Tuple = tuple()
Searches the list of tuples TupleList
for a
tuple whose N
th element compares equal to Key
.
Returns {value, Tuple}
if such a tuple is found,
otherwise false
.
Note!
This function is retained for backward compatibility.
The function lists:keyfind/3
(introduced in R13A)
is in most cases more convenient.
keysort(N, TupleList1) -> TupleList2
N = 1..tuple_size(Tuple)
TupleList1 = TupleList2 = [Tuple]
Tuple = tuple()
Returns a list containing the sorted elements of the list
TupleList1
. Sorting is performed on the N
th
element of the tuples.
keystore(Key, N, TupleList1, NewTuple) -> TupleList2
Key = term()
N = 1..tuple_size(Tuple)
TupleList1 = TupleList2 = [Tuple]
NewTuple = Tuple = tuple()
Returns a copy of TupleList1
where the first
occurrence of a tuple T
whose N
th element
compares equal to Key
is replaced with
NewTuple
, if there is such a tuple T
. If there
is no such tuple T
a copy of TupleList1
where
[NewTuple
] has been appended to the end is
returned.
keytake(Key, N, TupleList1) -> {value, Tuple, TupleList2} | false
Key = term()
N = 1..tuple_size(Tuple)
TupleList1 = TupleList2 = [Tuple]
Tuple = tuple()
Searches the list of tuples TupleList1
for a tuple
whose N
th element compares equal to Key
.
Returns {value, Tuple, TupleList2}
if such a tuple is
found, otherwise false
. TupleList2
is a copy
of TupleList1
where the first occurrence of
Tuple
has been removed.
last(List) -> Last
List = [term()], length(List) > 0
Last = term()
Returns the last element in List
.
map(Fun, List1) -> List2
Fun = fun(A) -> B
List1 = [A]
List2 = [B]
A = B = term()
Takes a function from A
s to B
s, and a list of
A
s and produces a list of B
s by applying
the function to every element in the list. This function is
used to obtain the return values. The evaluation order is
implementation dependent.
mapfoldl(Fun, Acc0, List1) -> {List2, Acc1}
Fun = fun(A, AccIn) -> {B, AccOut}
Acc0 = Acc1 = AccIn = AccOut = term()
List1 = [A]
List2 = [B]
A = B = term()
mapfold
combines the operations of map/2
and
foldl/3
into one pass. An example, summing
the elements in a list and double them at the same time:
>lists:mapfoldl(fun(X, Sum) -> {2*X, X+Sum} end,
0, [1,2,3,4,5]).
{[2,4,6,8,10],15}
mapfoldr(Fun, Acc0, List1) -> {List2, Acc1}
Fun = fun(A, AccIn) -> {B, AccOut}
Acc0 = Acc1 = AccIn = AccOut = term()
List1 = [A]
List2 = [B]
A = B = term()
mapfold
combines the operations of map/2
and
foldr/3
into one pass.
max(List) -> Max
List = [term()], length(List) > 0
Max = term()
Returns the first element of List
that compares
greater than or equal to all other elements of
List
.
member(Elem, List) -> bool()
Elem = term()
List = [term()]
Returns true
if Elem
matches some element of
List
, otherwise false
.
merge(ListOfLists) -> List1
ListOfLists = [List]
List = List1 = [term()]
Returns the sorted list formed by merging all the sub-lists
of ListOfLists
. All sub-lists must be sorted prior to
evaluating this function. When two elements compare equal,
the element from the sub-list with the lowest position in
ListOfLists
is picked before the other element.
merge(List1, List2) -> List3
List1 = List2 = List3 = [term()]
Returns the sorted list formed by merging List1
and
List2
. Both List1
and List2
must be
sorted prior to evaluating this function. When two elements
compare equal, the element from List1
is picked
before the element from List2
.
merge(Fun, List1, List2) -> List3
Fun = fun(A, B) -> bool()
List1 = [A]
List2 = [B]
List3 = [A | B]
A = B = term()
Returns the sorted list formed by merging List1
and
List2
. Both List1
and List2
must be
sorted according to the ordering function
Fun
prior to evaluating this function. Fun(A,
B)
should return true
if A
compares less
than or equal to B
in the ordering, false
otherwise. When two elements compare equal, the element from
List1
is picked before the element from
List2
.
merge3(List1, List2, List3) -> List4
List1 = List2 = List3 = List4 = [term()]
Returns the sorted list formed by merging List1
,
List2
and List3
. All of List1
,
List2
and List3
must be sorted prior to
evaluating this function. When two elements compare equal,
the element from List1
, if there is such an element,
is picked before the other element, otherwise the element
from List2
is picked before the element from
List3
.
min(List) -> Min
List = [term()], length(List) > 0
Min = term()
Returns the first element of List
that compares
less than or equal to all other elements of
List
.
nth(N, List) -> Elem
N = 1..length(List)
List = [term()]
Elem = term()
Returns the N
th element of List
. For example:
> lists:nth(3, [a, b, c, d, e]).
c
nthtail(N, List1) -> Tail
N = 0..length(List1)
List1 = Tail = [term()]
Returns the N
th tail of List
, that is, the sublist of
List
starting at N+1
and continuing up to
the end of the list. For example:
>lists:nthtail(3, [a, b, c, d, e]).
[d,e] >tl(tl(tl([a, b, c, d, e]))).
[d,e] >lists:nthtail(0, [a, b, c, d, e]).
[a,b,c,d,e] >lists:nthtail(5, [a, b, c, d, e]).
[]
partition(Pred, List) -> {Satisfying, NonSatisfying}
Pred = fun(Elem) -> bool()
Elem = term()
List = Satisfying = NonSatisfying = [term()]
Partitions List
into two lists, where the first list
contains all elements for which Pred(Elem)
returns
true
, and the second list contains all elements for
which Pred(Elem)
returns false
.
Examples:
>lists:partition(fun(A) -> A rem 2 == 1 end, [1,2,3,4,5,6,7]).
{[1,3,5,7],[2,4,6]} >lists:partition(fun(A) -> is_atom(A) end, [a,b,1,c,d,2,3,4,e]).
{[a,b,c,d,e],[1,2,3,4]}
See also splitwith/2
for a different way to partition
a list.
prefix(List1, List2) -> bool()
List1 = List2 = [term()]
Returns true
if List1
is a prefix of
List2
, otherwise false
.
reverse(List1) -> List2
List1 = List2 = [term()]
Returns a list with the top level elements in List1
in reverse order.
reverse(List1, Tail) -> List2
List1 = Tail = List2 = [term()]
Returns a list with the top level elements in List1
in reverse order, with the tail Tail
appended. For
example:
> lists:reverse([1, 2, 3, 4], [a, b, c]).
[4,3,2,1,a,b,c]
seq(From, To) -> Seq
seq(From, To, Incr) -> Seq
From = To = Incr = int()
Seq = [int()]
Returns a sequence of integers which starts with From
and contains the successive results of adding Incr
to
the previous element, until To
has been reached or
passed (in the latter case, To
is not an element of
the sequence). Incr
defaults to 1.
Failure: If To<From-Incr
and Incr
is positive, or if To>From-Incr
and Incr
is
negative, or if Incr==0
and From/=To
.
The following equalities hold for all sequences:
length(lists:seq(From, To)) == To-From+1 length(lists:seq(From, To, Incr)) == (To-From+Incr) div Incr
Examples:
>lists:seq(1, 10).
[1,2,3,4,5,6,7,8,9,10] >lists:seq(1, 20, 3).
[1,4,7,10,13,16,19] >lists:seq(1, 0, 1).
[] >lists:seq(10, 6, 4).
[] >lists:seq(1, 1, 0).
[1]
sort(List1) -> List2
List1 = List2 = [term()]
Returns a list containing the sorted elements of
List1
.
sort(Fun, List1) -> List2
Fun = fun(Elem1, Elem2) -> bool()
Elem1 = Elem2 = term()
List1 = List2 = [term()]
Returns a list containing the sorted elements of
List1
, according to the ordering function
Fun
. Fun(A, B)
should return true
if
A
compares less than or equal to B
in the
ordering, false
otherwise.
split(N, List1) -> {List2, List3}
N = 0..length(List1)
List1 = List2 = List3 = [term()]
Splits List1
into List2
and List3
.
List2
contains the first N
elements and
List3
the rest of the elements (the N
th tail).
splitwith(Pred, List) -> {List1, List2}
Pred = fun(Elem) -> bool()
Elem = term()
List = List1 = List2 = [term()]
Partitions List
into two lists according to
Pred
. splitwith/2
behaves as if it is defined
as follows:
splitwith(Pred, List) -> {takewhile(Pred, List), dropwhile(Pred, List)}.
Examples:
>lists:splitwith(fun(A) -> A rem 2 == 1 end, [1,2,3,4,5,6,7]).
{[1],[2,3,4,5,6,7]} >lists:splitwith(fun(A) -> is_atom(A) end, [a,b,1,c,d,2,3,4,e]).
{[a,b],[1,c,d,2,3,4,e]}
See also partition/2
for a different way to partition
a list.
sublist(List1, Len) -> List2
List1 = List2 = [term()]
Len = int()
Returns the sub-list of List1
starting at position 1
and with (max) Len
elements. It is not an error for
Len
to exceed the length of the list -- in that case
the whole list is returned.
sublist(List1, Start, Len) -> List2
List1 = List2 = [term()]
Start = 1..(length(List1)+1)
Len = int()
Returns the sub-list of List1
starting at Start
and with (max) Len
elements. It is not an error for
Start+Len
to exceed the length of the list.
>lists:sublist([1,2,3,4], 2, 2).
[2,3] >lists:sublist([1,2,3,4], 2, 5).
[2,3,4] >lists:sublist([1,2,3,4], 5, 2).
[]
subtract(List1, List2) -> List3
List1 = List2 = List3 = [term()]
Returns a new list List3
which is a copy of
List1
, subjected to the following procedure: for each
element in List2
, its first occurrence in List1
is deleted. For example:
> lists:subtract("123212", "212").
"312".
lists:subtract(A, B)
is equivalent to A -- B
.
Warning!
The complexity of lists:subtract(A, B)
is proportional
to length(A)*length(B)
, meaning that it will be very slow if
both A
and B
are long lists.
(Using ordered lists and
ordsets:subtract/2
is a much better choice if both lists are long.)
suffix(List1, List2) -> bool()
Returns true
if List1
is a suffix of
List2
, otherwise false
.
sum(List) -> number()
List = [number()]
Returns the sum of the elements in List
.
takewhile(Pred, List1) -> List2
Pred = fun(Elem) -> bool()
Elem = term()
List1 = List2 = [term()]
Takes elements Elem
from List1
while
Pred(Elem)
returns true
, that is,
the function returns the longest prefix of the list for which
all elements satisfy the predicate.
ukeymerge(N, TupleList1, TupleList2) -> TupleList3
N = 1..tuple_size(Tuple)
TupleList1 = TupleList2 = TupleList3 = [Tuple]
Tuple = tuple()
Returns the sorted list formed by merging TupleList1
and TupleList2
. The merge is performed on the
N
th element of each tuple. Both TupleList1
and
TupleList2
must be key-sorted without duplicates
prior to evaluating this function. When two tuples compare
equal, the tuple from TupleList1
is picked and the
one from TupleList2
deleted.
ukeysort(N, TupleList1) -> TupleList2
N = 1..tuple_size(Tuple)
TupleList1 = TupleList2 = [Tuple]
Tuple = tuple()
Returns a list containing the sorted elements of the list
TupleList1
where all but the first tuple of the
tuples comparing equal have been deleted. Sorting is
performed on the N
th element of the tuples.
umerge(ListOfLists) -> List1
ListOfLists = [List]
List = List1 = [term()]
Returns the sorted list formed by merging all the sub-lists
of ListOfLists
. All sub-lists must be sorted and
contain no duplicates prior to evaluating this function.
When two elements compare equal, the element from the
sub-list with the lowest position in ListOfLists
is
picked and the other one deleted.
umerge(List1, List2) -> List3
List1 = List2 = List3 = [term()]
Returns the sorted list formed by merging List1
and
List2
. Both List1
and List2
must be
sorted and contain no duplicates prior to evaluating this
function. When two elements compare equal, the element from
List1
is picked and the one from List2
deleted.
umerge(Fun, List1, List2) -> List3
Fun = fun(A, B) -> bool()
List1 = [A]
List2 = [B]
List3 = [A | B]
A = B = term()
Returns the sorted list formed by merging List1
and
List2
. Both List1
and List2
must be
sorted according to the ordering function
Fun
and contain no duplicates prior to evaluating
this function. Fun(A, B)
should return true
if
A
compares less than or equal to B
in the
ordering, false
otherwise. When two elements compare
equal, the element from
List1
is picked and the one from List2
deleted.
umerge3(List1, List2, List3) -> List4
List1 = List2 = List3 = List4 = [term()]
Returns the sorted list formed by merging List1
,
List2
and List3
. All of List1
,
List2
and List3
must be sorted and contain no
duplicates prior to evaluating this function. When two
elements compare equal, the element from List1
is
picked if there is such an element, otherwise the element
from List2
is picked, and the other one deleted.
unzip(List1) -> {List2, List3}
List1 = [{X, Y}]
List2 = [X]
List3 = [Y]
X = Y = term()
"Unzips" a list of two-tuples into two lists, where the first list contains the first element of each tuple, and the second list contains the second element of each tuple.
unzip3(List1) -> {List2, List3, List4}
List1 = [{X, Y, Z}]
List2 = [X]
List3 = [Y]
List4 = [Z]
X = Y = Z = term()
"Unzips" a list of three-tuples into three lists, where the first list contains the first element of each tuple, the second list contains the second element of each tuple, and the third list contains the third element of each tuple.
usort(List1) -> List2
List1 = List2 = [term()]
Returns a list containing the sorted elements of
List1
where all but the first element of the elements
comparing equal have been deleted.
usort(Fun, List1) -> List2
Fun = fun(Elem1, Elem2) -> bool()
Elem1 = Elem2 = term()
List1 = List2 = [term()]
Returns a list which contains the sorted elements of
List1
where all but the first element of the elements
comparing equal according to the ordering function
Fun
have been deleted. Fun(A, B)
should return
true
if A
compares less than or equal to
B
in the ordering, false
otherwise.
zip(List1, List2) -> List3
List1 = [X]
List2 = [Y]
List3 = [{X, Y}]
X = Y = term()
"Zips" two lists of equal length into one list of two-tuples, where the first element of each tuple is taken from the first list and the second element is taken from corresponding element in the second list.
zip3(List1, List2, List3) -> List4
List1 = [X]
List2 = [Y]
List3 = [Z]
List3 = [{X, Y, Z}]
X = Y = Z = term()
"Zips" three lists of equal length into one list of three-tuples, where the first element of each tuple is taken from the first list, the second element is taken from corresponding element in the second list, and the third element is taken from the corresponding element in the third list.
zipwith(Combine, List1, List2) -> List3
Combine = fun(X, Y) -> T
List1 = [X]
List2 = [Y]
List3 = [T]
X = Y = T = term()
Combine the elements of two lists of equal length into one
list. For each pair X, Y
of list elements from the two
lists, the element in the result list will be
Combine(X, Y)
.
zipwith(fun(X, Y) -> {X,Y} end, List1, List2)
is
equivalent to zip(List1, List2)
.
Example:
> lists:zipwith(fun(X, Y) -> X+Y end, [1,2,3], [4,5,6]).
[5,7,9]
zipwith3(Combine, List1, List2, List3) -> List4
Combine = fun(X, Y, Z) -> T
List1 = [X]
List2 = [Y]
List3 = [Z]
List4 = [T]
X = Y = Z = T = term()
Combine the elements of three lists of equal length into one
list. For each triple X, Y, Z
of list elements from
the three lists, the element in the result list will be
Combine(X, Y, Z)
.
zipwith3(fun(X, Y, Z) -> {X,Y,Z} end, List1, List2, List3)
is equivalent to zip3(List1, List2, List3)
.
Examples:
>lists:zipwith3(fun(X, Y, Z) -> X+Y+Z end, [1,2,3], [4,5,6], [7,8,9]).
[12,15,18] >lists:zipwith3(fun(X, Y, Z) -> [X,Y,Z] end, [a,b,c], [x,y,z], [1,2,3]).
[[a,x,1],[b,y,2],[c,z,3]]
- all/2
- any/2
- append/1
- append/2
- concat/1
- delete/2
- dropwhile/2
- duplicate/2
- filter/2
- flatlength/1
- flatmap/2
- flatten/1
- flatten/2
- foldl/3
- foldr/3
- foreach/2
- keydelete/3
- keyfind/3
- keymap/3
- keymember/3
- keymerge/3
- keyreplace/4
- keysearch/3
- keysort/2
- keystore/4
- keytake/3
- last/1
- map/2
- mapfoldl/3
- mapfoldr/3
- max/1
- member/2
- merge/1
- merge/2
- merge/3
- merge3/3
- min/1
- nth/2
- nthtail/2
- partition/2
- prefix/2
- reverse/1
- reverse/2
- seq/2
- seq/3
- sort/1
- sort/2
- split/2
- splitwith/2
- sublist/2
- sublist/3
- subtract/2
- suffix/2
- sum/1
- takewhile/2
- ukeymerge/3
- ukeysort/2
- umerge/1
- umerge/2
- umerge/3
- umerge3/3
- unzip/1
- unzip3/1
- usort/1
- usort/2
- zip/2
- zip3/3
- zipwith/3
- zipwith3/4