Group an JavaScript objects in array in specific order

Question

I have an array:

var tracks = [
  { id: 0, vibe: "downtempo" },
  { id: 1, vibe: "midtempo"  },
  { id: 2, vibe: "uptempo"  },
  { id: 3, vibe: "uptempo"  },
  { id: 4, vibe: "midtempo" },
  { id: 5, vibe: "downtempo"  },
  { id: 6, vibe: "midtempo" },
  { id: 7, vibe: "midtempo"  },
  { id: 8, vibe: "uptempo"  },
  { id: 9, vibe: "uptempo"  },
  ... 
  { id: 100, vibe: "midtempo"  },
];

What is the best way to sort this array to group objects by 'vibe' and get such sequence:

 { id: 0, vibe: "downtempo" },
  { id: 5, vibe: "downtempo" },
  { id: 15, vibe: "downtempo"  },
  { id: 1, vibe: "midtempo"  },
  { id: 4, vibe: "midtempo" },
  { id: 6, vibe: "midtempo" },
  { id: 2, vibe: "uptempo"  },
  { id: 3, vibe: "uptempo"  },
  { id: 8, vibe: "uptempo"  },
  { id: 12, vibe: "downtempo" },
  { id: 25, vibe: "downtempo" },
  { id: 45, vibe: "downtempo"  },
  ...
  { id: 100, vibe: "uptempo"  },

Thank you!

Its not a dublicate. My question is about how to group by 3 and put it in order — Viktor Kushnir
– Viktor Kushnir, Commented Oct 27, 2018 at 16:23
group and sort, i need such sequence: downtempo, downtempo, downtempo, midtempo, midtempo, midtempo, uptempo, uptempo, uptempo, downtempo, downtempo, downtempo, midtempo, midtempo, midtempo, uptempo, uptempo, uptempo — Viktor Kushnir
– Viktor Kushnir, Commented Oct 27, 2018 at 17:09
you are right, the wanted order is different. but what have you tried? please supply a greater data set for testing. you may have a look here, too: minimal reproducible example — Nina Scholz
– Nina Scholz, Commented Oct 27, 2018 at 17:11

Nina Scholz · Accepted Answer · 2018-10-28 20:23:14Z

You could use sorting with map by using a temporary object with a hashtable for the same group array. Take from it the length of the used array as group for sorting.

The sorting happens with the group, key and index.

The result is mapped with index of the sorted temporary array.

var array = [{ id: 0, vibe: 'downtempo' }, { id: 1, vibe: 'midtempo' }, { id: 2, vibe: 'uptempo' }, { id: 3, vibe: 'uptempo' }, { id: 4, vibe: 'midtempo' }, { id: 5, vibe: 'downtempo' }, { id: 6, vibe: 'midtempo' }, { id: 7, vibe: 'midtempo' }, { id: 8, vibe: 'uptempo' }, { id: 9, vibe: 'uptempo' }, { id: 10, vibe: 'midtempo' }, { id: 15, vibe: 'downtempo' }, { id: 12, vibe: 'downtempo' }, { id: 25, vibe: 'downtempo' }, { id: 45, vibe: 'downtempo' }],
    size = 3,
    order = { downtempo: 1, midtempo: 2, uptempo: 3 },
    groups = Object.create(null),
    result = array
        .map(({ vibe, key = order[vibe] }, index) => ({
            group: Math.floor(((groups[key] = groups[key] || []).push(key) - 1) / size),
            key,
            index
         }))
        .sort((a, b) => a.group - b.group || a.key - b.key || a.index - b.index)
        .map(({ index }) => array[index]);

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

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