WolframLang: Misc List Operations

By Xah Lee. Date: . Last updated: .

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. Position 
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
Cut into sublist Partition 
x = Range[ 8 ];
Partition[ x, 2 ] === {{1, 2}, {3, 4}, {5, 6}, {7, 8}}

order

Sort
Sort
SortBy
SortBy
reverse
reverse
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
Ordering
return a list of integers that represent the ordering of the items. Ordering 
Ordering[ {a, c, b} ] === {1, 3, 2}

List

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