count ( ... seq quot: ( ... elt -- ... ? ) -- ... n )
Factor handbook » The language » Collections » Sequence operations » Sequence combinators

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Vocabulary
sequences

Inputs

seq	a sequence
quot	a quotation

Outputs

n	an integer

Word description
Efficiently returns the number of elements that the predicate quotation matches.

Examples

USING: math ranges sequences prettyprint ; 100 [1..b] [ even? ] count .
50

Definition

USING: kernel ;

IN: sequences

: count ( ... seq quot: ( ... elt -- ... ? ) -- ... n )
    [ 1 0 ? ] compose map-sum ; inline