Remove values in array equal to subsequent arguments

Question

I want this function to work and produce the array [1,1], why doesn't it work?

 function destroyer(arr) {
      return arr.reduce(function(a,b){
         if (arguments.slice(1).every(function(arg){
             return arg !== b;
         })) a.push(b);
         return a;
      }, []);
    }

destroyer([1, 2, 3, 1, 2, 3], 2, 3);

What does it produce instead, and why do you think it should return [1,1]? — Scott Hunter
– Scott Hunter, Commented Aug 6, 2015 at 23:24
function destroyer(arr) {var args = Array.prototype.slice.call(arguments, 1); // Save arguments in a closure return arr.reduce(function(a,b){ if (args.every(function(arg){ // Access them here return arg !== b; })) a.push(b); return a; }, []); } Thanks to Jan for clearing things up as well. — R678
– R678, Commented Aug 7, 2015 at 0:01

Oriol · Accepted Answer · 2015-08-06 23:37:50Z

3

I suggest

function destroyer(arr) {
  return [].slice.call(arguments, 1).reduce(function(arr, num) {
    return arr.filter(function(item) {
      return num !== item;
    });
  }, arr);
}

Or, in ES6,

function destroyer(arr, ...unwanted) {
  return unwanted.reduce((arr,num) => arr.filter(item => num !== item), arr);
}

edited Aug 6, 2015 at 23:37

answered Aug 6, 2015 at 23:25

Oriol

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2 Comments

Jan Over a year ago

This is of course much nicer, but it doesn't answer OP's question "why doesn't it work?"

Travis J Over a year ago

To note, using slice on arguments will prevent the V8 engine from optimizing.

Travis J · Accepted Answer · 2015-08-06 23:48:07Z

0

jsFiddle Demo

arguments is not an array. It is "array-like". You need to call the array prototype. Also, splice modifies the array each time it is called, so it should only be used once.

function destroyer(arr) {
  //access the array prototype,
  //splice first element off of argument array,
  //and store result
  var args = [].splice.call(arguments,1);
  return arr.reduce(function(p,c){
   //indexOf is an easy way to look for existence in an array
   if( args.indexOf(c) == -1 ) p.push(c);
   return p;
  }, []);
}

Calling this on your input, destroyer([1, 2, 3, 1, 2, 3], 2, 3) will result in [1,1].

answered Aug 6, 2015 at 23:48

Travis J

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1 Comment

R678 Over a year ago

Gotcha, was not aware that arguments is not technically an array.

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