WolframLang: Misc List Operations

By Xah Lee. Date: 2022-07-05. Last updated: 2023-09-27.

Check Existence

MemberQ: Check existence by Pattern
MemberQ
Count: Count by Pattern
Count

Get the Position of a Element

Position[expr, pattern]

Return a list of positions that Pattern occur in expression. If not exist, return a empty list.

xx = {a, {{b, c}, a}, e};

(* position of e is {3} *)
Position[ xx, e ] === {{3}}

(* position of a is {1} and {2, 2} *)
Position[ xx, a ] === {{1}, {2, 2}}

(* when not found, empty list *)
Position[ xx, m ] === {}

(* position of b *)
Position[ xx, b ] === {{2, 1, 1}}

(* position of {b, c} *)
Position[ xx, {b, c} ] === {{2, 1}}

Group into Sublists

Partition

group every n items into sublist.

Partition

x = Range[ 8 ];
Partition[ x, 2 ] === {{1, 2}, {3, 4}, {5, 6}, {7, 8}}

order

Sort: Sort
SortBy: SortBy
reverse: reverse

Ordering

return a list of integers that represent the ordering of the items.

Ordering

Ordering[ {a, c, b} ] === {1, 3, 2}

RotateRight

shift all elements to the right, last item is moved to first.

RotateRight

RotateRight[ {1, 2, 3, 4} ] === {4, 1, 2, 3}

RotateLeft

shift all elements to the left, first item is moved to last.

RotateLeft

Other Functions on List

Join: concatenate lists Join
Union: union of sets Union
Intersection: intersection of sets Intersection
Complement: subtract a set from other sets Complement
Subsets: all possible subsets Subsets

Riffle: Riffle
Partition: Partition

Split: Split
SplitBy: SplitBy
Gather: Gather
GatherBy: GatherBy

Tuples: Tuples

Permutations: Permutations

Min: Min
Max: Max

Flatten: Flatten
Transpose: Transpose
PadLeft: PadLeft