Prepend

The collection with value added as its first element.

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

Prepend(collection, value)the collection with value added as its first element.

Prepend(association, rule)association with rule (or a list of rules) inserted at the front; a prepended key displaces any later entry for the same key.

Typed signatures

Type	Package	Applies
(collection<any>, value) -> collection	combinatorics	always

Domain: Collections

Details

• $Prepend(c, x) = Join(\{x\}, c)$. See Join.
• Complements Append at the other end of a collection.

Examples

3 more kept as data, checked against the oracles

Basic #

live ↗

In$\mathrm{Prepend}(\bigl\lbrack a, b, c, d\bigr\rbrack, x)$Out$\bigl\lbrack x, a, b, c, d\bigr\rbrack$

Scope #

A rule inserted at the front of an association

live ↗

In$\mathrm{Prepend}(\mathrm{Association}(\mathrm{Rule}(1, a), \mathrm{Rule}(2, b)), \mathrm{Rule}(3, d))$Out$\mathrm{Association}(\mathrm{Rule}(3, d), \mathrm{Rule}(1, a), \mathrm{Rule}(2, b))$

Several rules prepended at once

live ↗

In$\mathrm{Prepend}(\mathrm{Association}(\mathrm{Rule}(1, a), \mathrm{Rule}(2, b)), \bigl\lbrack\mathrm{Rule}(3, d), \mathrm{Rule}(4, e)\bigr\rbrack)$Out$\mathrm{Association}(\mathrm{Rule}(3, d), \mathrm{Rule}(4, e), \mathrm{Rule}(1, a), \mathrm{Rule}(2, b))$

Applications #

Repeatedly prepending grows the list by one $x$ each step

live ↗

In$\mathrm{NestList}(\operatorname{\_1}↦\mathrm{Prepend}(\operatorname{\_1}, x), \bigl\lbrack a\bigr\rbrack, 5)$Out$\bigl\lbrack\bigl\lbrack a\bigr\rbrack, \bigl\lbrack x, a\bigr\rbrack, \bigl\lbrack x, x, a\bigr\rbrack, \bigl\lbrack x, x, x, a\bigr\rbrack, \bigl\lbrack x, x, x, x, a\bigr\rbrack, \bigl\lbrack x, x, x, x, x, a\bigr\rbrack\bigr\rbrack$

Properties #

$Prepend(c, x) = Join(\{x\}, c)$. See Join

live ↗

In$\mathrm{Prepend}(\bigl\lbrack1, 2, 3\bigr\rbrack, 0)=\mathrm{Join}(\bigl\lbrack0\bigr\rbrack, \bigl\lbrack1, 2, 3\bigr\rbrack)$Out$\mathrm{True}$

Possible issues #

A list argument is added as one element, not spliced in

live ↗

In$\mathrm{Prepend}(\bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack x, y\bigr\rbrack)$Out$\bigl\lbrack\bigl\lbrack x, y\bigr\rbrack, a, b, c\bigr\rbrack$

About

Examples	9
Checked against	Wolfram Language 8 agreemathlib4 4 agree
Crosswalk	Wolfram Language

Implementation

mappedmathlib4packages/oracle/src/mappings.ts

The value consed onto the list; a list value onto a list of scalars fails to elaborate (ours nests it as one element), as does an association.

See also: Append, Join