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Idiom #316 Count occurrences in a list

Determine the number c of elements in the list x that satisfy the predicate p.

let c = x.filter(p).length

Array.prototype.filter takes in a predicate function, and runs it for every element in the array, if the predicate returns true, the element is kept, but if not, the element is removed.

So, c is the length of the array returned by Array.prototype.filter.
  
c=count(p(x))

p has to be an elemental function with an argument of the type of x.
New implementation...
< > ⌨
programming-idioms.org 
let c = x.filter(p).length
  
c=count(p(x))
c := 0
for _, v := range x {
	if p(v) {
		c++
	}
}
func count[T any](x []T, p func(T) bool) int {
	c := 0
	for _, v := range x {
		if p(v) {
			c++
		}
	}
	return c
}
int c = frequency(x, p);
  c := 0;
  for el in x do if p(el) then Inc(c);
my $c = grep { p($_) } @x;
c = sum(p(v) for v in x)
c = x.count{|el| p(el) }