CODE EXAMPLE FOR JAVASCRIPT

javascript filter in place algorithm

function filterInPlace(a, condition, thisArg) {
  let j = 0;

  a.forEach((e, i) => { 
    if (condition.call(thisArg, e, i, a)) {
      if (i!==j) a[j] = e; 
      j++;
    }
  });

  a.length = j;
  return a;
}

a = [ 1,, 3 ];
document.write('<br>[',a,']');

filterInPlace(a, x=>true);
document.write('<br>[',a,'] compaction when nothing changed');

b = [ 1,,3,,5 ];
document.write('<br>[',b,']');

filterInPlace(b, x=>x!==5);
document.write('<br>[',b,'] with 5 removed');
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