lodash sortBy then groupBy, is order maintained?

Question

I\'m having trouble figuring out from the lodash documentation if my assumption about sorting and grouping is correct.

If I use sortBy, then use groupBy, do the arrays p

Answer 1

It's not. Here's example, where order is not retained:

const data = [
  {
    item: 'item1',
    group: 'g2'
  },   {
    item: 'item2',
    group: 'g3'
  },   {
    item: 'item3',
    group: 'g1'
  },   {
    item: 'item4',
    group: 'g2'
  },   {
    item: 'item5',
    group: 'g3'
  }
]

const groupedItems = _(data).groupBy(item => item.group).value()

In this case one would expect that group order would be: g2, g3, g1 - reality is that they are sorted g1, g2, g3.

You can re-sort them with original array though.

const groupedItems = _(data)
  .groupBy(item => item.group)
  .sortBy(group => data.indexOf(group[0]))
  .value()

This will ensure original order of items.