Filter array of objects using a list of desired key values

Question

I have an array of objects that might look like this:

var arr = [{
  a: 1,
  b: 321,
  c: 556,
  d: 8
}, {
  a: 1,
  b: 22,
  c: 21,
  d: 8
}, {
  a: 1,
  b: 1,
  c: 43,
  d: 8
}, ];

and another list that could be:

var list = ['a', 'c', 'd'];

Since my list only has keys a, c, and d I want to get rid of all instances of the b key on my original array. All this procedure has to be dynamic though because There is no way for me to know what those keys might be prior to receiving them.

Is there a nice and clean way of doing this in JavaScript?

You want to merge? Something like list = [1, 1, 1, 556, 21, 43, 8, 8, 8] ? — Rodmentou
– Rodmentou, Commented Oct 30, 2015 at 14:46
@ergonaut there is no need to post my code in this sort of question. I do not have an issue in doing it, so that someone then has to fix my code. I am more interested on if there is some js trick I am not aware of. If you would have seen my code then it would be identical to Siguza's minus James's suggestion. — dearn44
– dearn44, Commented Oct 30, 2015 at 14:52
judging from your comments, your definition of "clean" is that you want a js function that isn't in library that somehow does not involve loops. Then the answer is NO. — ergonaut
– ergonaut, Commented Oct 30, 2015 at 14:56

Siguza · Accepted Answer · 2015-10-30 14:49:11Z

1

arr.forEach(function(element)
{
    for(var key in element)
    {
        if(list.indexOf(key) === -1)
        {
            delete element[key];
        }
    }
});

Should be pretty self-explanatory.

If you don't want to modify the original array:

arr.map(function(element)
{
    element = JSON.parse(JSON.stringify(element));
    for(var key in element)
    {

        if(list.indexOf(key) === -1)
        {
            delete element[key];
        }
    }
    return element;
});

edited Oct 30, 2015 at 14:49

answered Oct 30, 2015 at 14:46

Siguza

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3 Comments

James Allardice Over a year ago

You could shorten this a bit by using arr.forEach since you're modifying the objects in place. No need to return anything then.

Siguza Over a year ago

@JamesAllardice Thanks for the hint, updated my answer.

dearn44 Over a year ago

Even though underscore is not a bad alternative I will go with this answer. I think it would be of more interest to someone visiting the thread in the future.

Jared Dykstra · Accepted Answer · 2015-11-06 21:37:37Z

1

Consider using the underscore.js library. It contains a reject method that should do the trick

reject _.reject(list, predicate, [context]) Returns the values in list without the elements that the truth test (predicate) passes. The opposite of filter.

var odds = _.reject([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });

=> [1, 3, 5]

edited Nov 6, 2015 at 21:37

answered Oct 30, 2015 at 14:45

Jared Dykstra

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2 Comments

misantronic Over a year ago

_.reject is awesome!

dearn44 Over a year ago

I sort of have a feeling that i the end I will go with underscore, but I hoped to not have to depend to it.

misantronic · Accepted Answer · 2015-10-30 14:58:52Z

0

Is that what you're looking for?

for(var i=0, i < arr.length; i++) {
  if(arr[i].b) delete arr[i].b
}

// Update, a vanilla approach

var reject = [ "b" ];
for(var i=0, i < arr.length; i++) {
  for(var j in arr[i]) {
    if(reject.indexOf(j) != -1) delete arr[i][j];
  }
}

edited Oct 30, 2015 at 14:58

answered Oct 30, 2015 at 14:46

misantronic

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1 Comment

dearn44 Over a year ago

This cannot be it because it has to be dynamic. If we make your solution dynamic then it becomes similar to Siguza's.

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