Reduce array of objects on key and sum value into array

Question

I have the following object:

data = [
  { name: 'foo', type: 'fizz', val: 9 },
  { name: 'foo', type: 'buzz', val: 3 },
  { name: 'bar', type: 'fizz', val: 4 },
  { name: 'bar', type: 'buzz', val: 7 },
];

And used lodash map:

result = _.map(data, function item, idx){
  return {
    key: item[key],
    values: item.value,
  }
}

Which results in:

[
  { key: foo, val: 9 },
  { key: foo, val: 3 },
  { key: bar, val: 4 },
  { key: bar, val: 7 },
]

but now I'm trying to return:

[
  { key: 'foo', val: 12 },
  { key: 'bar', val: 11 },
]

I tried using reduce which seems to only output to a single object, which I could then convert back into an array, but I feel like there must be an elegant way to use lodash to go from my source data straight to my desired result without all of the intermediate steps.

I thought this was addressing my exact problem, but it seems like quite a bit of work just to have to convert the object into the desired array of objects outlined above.

Cheers.

Answer 1

A twist to the accepted answer that uses groupBy instead of reduce to do the initial grouping:

var result = _.chain(data)
    .groupBy('name')
    .map((group, key) => ({ key, val : _.sumBy(group, 'val') }))
    .value();