# WolframLang: Misc List Operations

By Xah Lee. Date: . Last updated: .

## Check Existence

`MemberQ`
Check existence by Pattern
`Count`
Count by Pattern

## 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}}

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

## order

`Sort`
`SortBy`
`reverse`
`Ordering`
return a list of integers that represent the ordering of the items.
`Ordering[ {a, c, b} ] === {1, 3, 2}`
`RotateRight`
shift all elements to the right, last item is moved to first.
`RotateRight[ {1, 2, 3, 4} ] === {4, 1, 2, 3}`
`RotateLeft`
shift all elements to the left, first item is moved to last.

## 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`