Association

A keyed collection of rules key -> value.

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Association(k1 -> v1, …)a key -> value map, built from

Rule

pairs.

Typed signatures

Type	Package	Applies
`(rules: expression<Rule>*) -> any`	`combinatorics`	always

Domain: Collections

Details

Its own operator, not compute-engine's $Dictionary$ : $Dictionary$ 's keys are strings only, and every example here keys on a plain number.
Length, First, Last, Join and Sort are extended to recognize an $Association$ and answer in terms of its values, falling through to their ordinary list handling otherwise.
Not a general replacement for $Dictionary$ or a full port of Wolfram's Association: only the operations the examples below exercise are implemented.

Examples

Basic #

Length counts the key-value pairs

In

\mathrm{Length}(\mathrm{Association}(\mathrm{Rule}(1, 2), \mathrm{Rule}(3, 4)))

Out

2

First is the first value, not the first rule

In

\mathrm{First}(\mathrm{Association}(\mathrm{Rule}(1, a), \mathrm{Rule}(2, b)))

Out

a

Last is the last value

In

\mathrm{Last}(\mathrm{Association}(\mathrm{Rule}(1, a), \mathrm{Rule}(2, b)))

Out

b

Scope #

Join merges keys; a later value for a repeated key wins, in the key's original position

In

\mathrm{Join}(\mathrm{Association}(\mathrm{Rule}(a, b)), \mathrm{Association}(\mathrm{Rule}(c, d), \mathrm{Rule}(a, f)))

Out

\mathrm{Association}(\mathrm{Rule}(a, f), \mathrm{Rule}(c, d))

Sort orders the entries by value

In

\mathrm{Sort}(\mathrm{Association}(\mathrm{Rule}(a, 4), \mathrm{Rule}(b, 1), \mathrm{Rule}(c, 3)))

Out

\mathrm{Association}(\mathrm{Rule}(b, 1), \mathrm{Rule}(c, 3), \mathrm{Rule}(a, 4))

About

Examples	5
Checked against	Wolfram Language 5 agree
Crosswalk	Wolfram Language

See also: Length, First, Last, Join, Sort