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Idiom #57 Filter list

Create list y containing items from list x satisfying predicate p. Respect original ordering. Don't modify x in-place.

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(e => e == p).ToList();
var y = x.FindAll(p);
import std.algorithm;
auto y = [1, 2, 3, 4, 5].filter!(a => a%2==0);

import std.algorithm.iteration;
auto y = x.filter!(p);
var y = x.where(p).toList();
y = for item <- x, p.(item), do: item
y = Enum.filter(x, p)
Y = [I || I <- X, P(X)].
Y = lists:filter(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)
	}
}
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))
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Related idioms

for Item of X loop
   if P (Item) then
      Y.Append (Item);
   end if;
end loop;
(def y (filter p x))
std::copy_if (x.begin (), x.end (), std::back_inserter(y), p);

var y = x.Where(e => e == p).ToList();
var y = x.FindAll(p);
auto y = [1, 2, 3, 4, 5].filter!(a => a%2==0);

auto y = x.filter!(p);
var y = x.where(p).toList();
y = for item <- x, p.(item), do: item
y = Enum.filter(x, p)
Y = [I || I <- X, P(X)].
Y = lists:filter(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)
	}
}
def y = x.findAll(p)
y = filter p x

y = x.filter(p);
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
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))