Chunks of an Array of objects using an object property as the "delimiter"

Question

Given the following array:

var arr = [{id:1 , code:0},
           {id:1 , code:12},
           {id:1 , code:0},
           {id:1 , code:0},
           {id:1 , code:5}];

How can I use lodash, to split the array each time code is not equal to 0 and get the following results?

[
 [{id:1 , code:0},{id:1 , code:12}],
 [{id:1 , code:0},{id:1 , code:0},{id:1 , code:5}]
]

I can suggest a short working solution on pure JS, if you're interested — RomanPerekhrest, Aug 30 '16 at 11:42

Ori Drori · Accepted Answer · 2016-08-30T16:40:48.753

4

You can use Array.prototype.reduce (or lodash's _.reduce()) for this:

var arr = [{id:1 , code:0},
           {id:1 , code:12},
           {id:1 , code:0},
           {id:1 , code:0},
           {id:1 , code:5}];

var result = arr.reduce(function(result, item, index, arr) {
  index || result.push([]); // if 1st item add sub array
  
  result[result.length - 1].push(item); // add current item to last sub array
  
  item.code !== 0 && index < arr.length - 1 && result.push([]); // if the current item code is not 0, and it's not the last item in the original array, add another sub array
  
  return result;
}, []);

console.log(result);

edited Aug 30 '16 at 16:40

answered Aug 30 '16 at 11:45

Ori Drori

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You can get rid of `index || result.push([]);` if you just start the reduce with `[[]]` – Joe Thomas Feb 23 '19 at 05:51
Nope - if the original array is empty, the result would be `[[]]`. – Ori Drori Feb 23 '19 at 08:06

score 3 · Answer 2 · answered Aug 30 '16 at 11:51

A solution in plain Javascript with a single loop without mutating the original array.

var arr = [{ id: 1, code: 0 }, { id: 1, code: 12 }, { id: 1, code: 0 }, { id: 1, code: 0 }, { id: 1, code: 5 }],
    grouped = arr.reduce(function (r, a, i) {
        var l = r[r.length - 1];
        if (!i || l[l.length - 1].code) {
            r.push([a]);
        } else {
            l.push(a);
        }
        return r;
    }, []);

console.log(grouped)

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score 0 · Answer 3 · answered Aug 30 '16 at 11:47

An alternative "native" JS solution using Array.splice function:

var arr = [{id:1 , code:0},{id:1 , code:12}, {id:1 , code:0},{id:1 , code:0}, {id:1 , code:5}],
    chunks = [];

for (var i = 0; i < arr.length; i++) {
    arr[i].code !== 0 && chunks.push(arr.splice(0, i + 1));
}

console.log(JSON.stringify(chunks, 0, 4));

score 0 · Answer 4 · answered Aug 30 '16 at 13:16

Well in the result if you expect reduced number elements then i guess you just have to reduce.

var arr = [{id:1 , code:0},
           {id:1 , code:12},
           {id:1 , code:0},
           {id:1 , code:0},
           {id:1 , code:5}],
reduced = arr.reduce((red,obj) => !obj.code ? red[red.length-1].length === 1 ||
                                              red[red.length-1].length === 0 ? (red[red.length-1].push(obj),red)
                                                                             : red.concat([[obj]])
                                            : (red[red.length-1].push(obj),red),[[]]);
console.log(reduced);

Chunks of an Array of objects using an object property as the "delimiter"

4 Answers4