function
boot.janet on line 1141, column 1
(keep pred ind & inds)
Given a predicate `pred`, return a new array containing the truthy
results of applying `pred` to each value in the data structure
`ind`, but only if no `inds` are provided. Multiple data structures
can be handled if each `inds` is a data structure and `pred` is a
function of arity one more than the number of `inds`. The resulting
array has a length that is no longer than the shortest of `ind` and
each of `inds`.
# 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]