Extract

The part of expr at position pos, or a list of parts at several positions.

✓ checked against that system · ! checked, with disagreements (hover a chip)Wolfram LanguageExtract✓↗

Extract(expr, pos)the part at pos — a bare integer, or a {i, j, …} path drilling into nested operands

Extract(expr, {{pos1}, {pos2}, …})the LIST of parts at each of several positions, one per element

Typed signatures

Type	Package	Applies
(any, any) -> any	combinatorics	always

Domain: Collections

Details

• Same 1-based, negative-counts-from-the-end indexing as At/Part.
• Disambiguated Wolfram's own way: pos is a single path unless every one of its own elements is itself a List, in which case it's a list of paths.
• Extract(expr, {}) is expr itself — the trivial, zero-step path.

Examples

Basic #

live ↗

In$\mathrm{Extract}(\bigl\lbrack\bigl\lbrack a, b\bigr\rbrack, \bigl\lbrack c, d\bigr\rbrack\bigr\rbrack, \bigl\lbrack2, 1\bigr\rbrack)$Out$c$

A one-element position list picks out that single part

live ↗

In$\mathrm{Extract}(\bigl\lbrack1, 2, 3, 4\bigr\rbrack, \bigl\lbrack2\bigr\rbrack)$Out$2$

Scope #

live ↗

In$\mathrm{Extract}(\bigl\lbrack a, b, c\bigr\rbrack, -1)$Out$c$

live ↗

In$\mathrm{Extract}(\bigl\lbrack\bigl\lbrack a, b\bigr\rbrack, \bigl\lbrack c, d\bigr\rbrack\bigr\rbrack, \bigl\lbrack\bigl\lbrack1, 1\bigr\rbrack, \bigl\lbrack2, 2\bigr\rbrack\bigr\rbrack)$Out$\bigl\lbrack a, d\bigr\rbrack$

live ↗

In$\mathrm{Extract}(\bigl\lbrack a, b, c, d, k\bigr\rbrack, \bigl\lbrack3\bigr\rbrack)$Out$c$

live ↗

In$\mathrm{Extract}(\bigl\lbrack a, b, c, d, k\bigr\rbrack, \bigl\lbrack\bigl\lbrack1\bigr\rbrack, \bigl\lbrack4\bigr\rbrack, \bigl\lbrack3\bigr\rbrack\bigr\rbrack)$Out$\bigl\lbrack a, d, c\bigr\rbrack$

About

Examples	6
Checked against	Wolfram Language 6 agree
Crosswalk	Wolfram Language

See also: ReplacePart, Level