Lodash has a nice chunk method for arrays; is there an equivalent for objects (associative arrays)? The imperative solution is pretty straight forward, but I'm just curious if there is a cleaner functional implementation?

Imperative solution:
Takes an object as input
Returns an array of objects with size number of properties

var chunk = function(input, size){
  var obj = {};
  var output = [];
  var counter = 0;
  for (var k in input) {
    if(!input.hasOwnProperty(k)){
      continue;
    }
    obj[k] = input[k];
    if (++counter % size === 0) {
      output.push(obj);
      obj = {};
    }
  }
  if (Object.keys(obj).length !== 0){
    output.push(obj);
  }
  return output;
};

Lodash has a nice chunk method for arrays; is there an equivalent for objects (associative arrays)? The imperative solution is pretty straight forward, but I'm just curious if there is a cleaner functional implementation?

Imperative solution:
Takes an object as input
Returns an array of objects with size number of properties

var chunk = function(input, size){
  var obj = {};
  var output = [];
  var counter = 0;
  for (var k in input) {
    if(!input.hasOwnProperty(k)){
      continue;
    }
    obj[k] = input[k];
    if (++counter % size === 0) {
      output.push(obj);
      obj = {};
    }
  }
  if (Object.keys(obj).length !== 0){
    output.push(obj);
  }
  return output;
};

• javascript
• functional-programming
• lodash

• 3 Maybe you could use _.pairs, then chunk, and _.object at the end? – Platinum Azure Commented Jul 31, 2015 at 16:40

2 Answers 2

_.mixin({"chunkObj": function(input, size) {
    return _.chain(input).pairs().chunk(size).map(_.object).value();
}});

console.log(_.chunkObj({a:1,b:2,c:3,d:4,e:5}, 2))

When I used with my array, I found it was causing the second and third sections to be mapped differently.

var skills = {};
skills["administration"] = 0;
skills["mechanical-engineering"] = 0;
skills["zero-g-operations"] = 0;

A sample object from the first object from the chunkObj looks like:

0: administration: 0

Using a 3-way split, the second and third chunkObj response however looks like

1: mechanical-engineering,0:undefined
2: zero-g-operations,0:undefined

My fixed method that keeps chunks 2 and 3 the same as the first:

_.mixin({"chunkObj": function(input, size) {
    var chunked = _.chunk(_.keys(input), size);
    var ret = {};   
    _.each(chunked, function(key, i) {
        var chunkedObj = {};
        _.each(chunked[i], function(key) {
            chunkedObj[key] = input[key];
        });
        ret[i] = chunkedObj;
    }); 
    return ret;
}});

In this case, the third section correctly bees

0: administration: 0
1: mechanical-engineering: 0
2: zero-g-operations: 0