function
boot.janet on line 978, column 1
(keep pred ind)
Given a predicate `pred`, return a new array containing the truthy
results of applying `pred` to each element in the indexed
collection `ind`. This is different from `filter` which returns an
array of the original elements where the predicate is truthy.
# absolute value of negatives, ignore positives
(keep |(if (< $ 0) (- $) nil) [-1 2 -3 -4 -5 6]) # -> @[1 3 4 5]
# halves each even number, ignores odds
(keep |(when (even? $) (/ $ 2)) [1 2 8 7 -2]) # -> @[1 4 -1]
(def person-ids {"Alice" 42 "Bob" 23})
(keep person-ids ["Carl" "Bob" "Alice"]) # -> @[23 42]
(filter person-ids ["Carl" "Bob" "Alice"]) # -> @["Bob" "Alice"]
(map person-ids ["Carl" "Bob" "Alice"]) # -> @[nil 23 42]