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Programming-Idioms

Create the list y containing the items from the list x that satisfy the predicate p. Respect the original ordering. Don't modify x in-place.
New implementation

Be concise.

Be useful.

All contributions dictatorially edited by webmasters to match personal tastes.

Please do not paste any copyright violating material.

Please try to avoid dependencies to third-party libraries and frameworks.

Other implementations
for Item of X loop
   if P (Item) then
      Y.Append (Item);
   end if;
end loop;
(def y (filter p x))
#include <algorithm>
#include <iterator>
std::copy_if (x.begin (), x.end (), std::back_inserter(y), p);
using System.Linq;
var y = x.Where(p).ToList();
var y = x.FindAll(p);
import std.algorithm.iteration;
auto y = x.filter!(p);
import std.algorithm;
auto y = [1, 2, 3, 4, 5].filter!(a => a%2==0);
var y = x.where(p).toList();
y = for item <- x, p.(item), do: item
y = Enum.filter(x, p)
Y = lists:filter(P, X).
Y = [I || I <- X, P(X)].
y = pack(x,mask=p(x))
y := make([]T, 0, len(x))
for _, v := range x{
	if p(v){
		y = append(y, v)
	}
}
n := 0
for _, v := range x {
	if p(v) {
		n++
	}
}
y := make([]T, 0, n)
for _, v := range x {
	if p(v) {
		y = append(y, v)
	}
}
func filter[S ~[]T, T any](x S, p func(T) bool) S {
	var y S
	for _, v := range x {
		if p(v) {
			y = append(y, v)
		}
	}
	return y
}
import "slices"
del := func(t *T) bool { return !p(t) }

y := slices.DeleteFunc(slices.Clone(x), del)
def y = x.findAll(p)
y = filter p x
y = x.filter(p);
import java.util.stream.Collectors;
var y = x.stream().filter(p).collect(Collectors.toList());
val y = x.filter(p)
(setf y (remove-if-not p x))
y = {}
for _, v in ipairs(x) do
	if p(v) then y[#y+1] = v end
end
@import Foundation;
NSArray *y=[x filteredArrayUsingPredicate:p];
function p($element) {  /* .... */ }

$y = array_filter ($x, "p");
function Filter(vv:integer):boolean;

begin
  result :=  vv mod 2= 0;
end;

type TFilter=function(v:integer):boolean;

function FilteredArray(const x:TBoundArray;p:TFilter):TBoundArray;
var
  Idx: Integer;
  v : Integer;

begin
  setlength(result,high(x)+1);
  Idx := 0;
  for v in x do
    if p(v) then
    begin
      result[Idx] := v;
      inc(Idx);
    end;
  setlength(result,Idx);
end;
[...]
  y := FilteredArray(x,@Filter);
# You can use a subroutine as your predicate
@primes_less_than_100 = grep { is_prime($_) } 1 .. 99;

# You can also write your predicate inline
@odd_numbers = grep { $_%2 == 1 } 1 .. 99;
y = [element for element in x if p(element)]
y = list(filter(p, x))
y = x.select(&:p)
let y: Vec<_> = x.iter().filter(p).collect();
val y = x.filter(p)
(define y (filter p x))
y := x select: [:item | item p].