function
boot.janet on line 1264 , column 1
(count pred x & xs )
Count the number of values in `x` for which applying `pred` yields
a truthy value.
Also functions variadically , i.e. takes additional arguments , with
suitable changes to the arity of `pred` . `pred` is called with both
values from `x` and additional arguments , and only as many times as
the length of the shortest of `x` and each element of `xs` . If `x`
or any element of `xs` is empty , returns 0.
`x` and elements of `xs` can be values of type bytes , indexed ,
dictionary , fiber , or abstract with suitable `get` and `next`
methods.
(count even? [1 2 3 4 5 ]) # => 2
(count (fn [x ] (> x 3 )) [1 2 3 4 5 ]) # => 2
(count |(> $ 3 ) [1 2 3 4 5 ]) # => 2
(count (fn [x ] (truthy? x )) [nil false true 42 :a "foo" ]) # => 4
(count |(truthy? $ ) [nil false true 42 :a "foo" ]) # => 4
(var f even? )
(count f [1 2 3 4 5 ]) # => 2
(set f odd? )
(count f [1 2 3 4 5 ]) # => 3
(map (fn [f ] (count f [1 2 3 4 5 ])) [even? odd? ]) # => @[2 3]
(map |(count $ [1 2 3 4 5 ]) [even? odd? ]) # => @[2 3]