How to deep filter objects (not object arrays)

Question

I'm working with a JS data structure that looks something like this:

table = {
  row1: {
    col1: 'A',
    col2: 'B',
    col3: 'C'
  },
  row2: {
    col1: 'D',
    col2: 'A',
    col3: 'F'
  },
  row3: {
    col1: 'E',
    col2: 'G',
    col3: 'C'
  }
};

How would you guys filter this object using JavaScript's native filter/map/reduce functions to produce an array of row object keys that contain the property col3 = "C"?

In this case, it would return ['row1', 'row3'].

This is a solution that I originally came up with based on another answer:

Object.keys(Object.keys(table).reduce(function(accumulator, currentValue) {
  if (table[currentValue].col3==='C') accumulator[currentValue] = table[currentValue];
  return accumulator;
}, {}));

However, I have accepted the solution below using filter() because it's more efficient. The accepted answer is in ES6 syntax, but ES5 syntax was provided by @Paulpro:

Object.keys(table).filter(function(row) {
  return table[row].col3==='C';
});

(Note that there are similar solutions out there, but they use custom functions and are not as concise as the accepted answer provided below.)

How would you do it? Where's your code? Where are you stuck? — user2437417
– user2437417, Commented Apr 24, 2018 at 23:32
Possible duplicate of Search a javascript object for a property with a specific value? — Heretic Monkey
– Heretic Monkey, Commented Apr 24, 2018 at 23:47
@MikeMcCaughan the solution using filter() provided here is more concise than the solutions for the linked question. — thdoan
– thdoan, Commented Apr 25, 2018 at 9:03
@CrazyTrain the solution I came up with was not as elegant as the accepted answer (but I didn't have it when I posted the question originally, or else I would've never posed the question): Object.keys(Object.keys(table).reduce(function(accumulator, currentValue) { if (table[currentValue].col3==='C') accumulator[currentValue] = table[currentValue]; return accumulator; }, {})); — thdoan
– thdoan, Commented Apr 25, 2018 at 9:17

dave · Accepted Answer · 2018-04-24 23:43:56Z

2

You could use Object.keys and then filter using the original object:

table = {
  row1: {
    col1: 'A',
    col2: 'B',
    col3: 'C'
  },
  row2: {
    col1: 'D',
    col2: 'A',
    col3: 'F'
  },
  row3: {
    col1: 'E',
    col2: 'G',
    col3: 'C'
  }
};

console.log(Object.keys(table).filter(function(t) { return table[t].col3 === 'C'}))

edited Apr 24, 2018 at 23:43

answered Apr 24, 2018 at 23:32

dave

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4 Comments

thdoan Over a year ago

Thanks @dave. This is elegant, but cannot rely on ES6 -- can you please provide ES5 version?

Paul Over a year ago

He asked for ES5, so you should probably avoid using an arrow function.

Paul Over a year ago

@thdoan Object.keys and Array.prototype.filter are both ES5 so you just need to replace the arrow function with a normal function. It doesn't use this so it can be swapped out directly: function ( t ) { return table[t].col3 === 'C'; }

thdoan Over a year ago

Thanks for the quick help, guys 8). I'll accept dave using ES5 revision from @Paulpro: Object.keys(table).filter(function ( t ) { return table[t].col3 === 'C'; })

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