sum up object properties in array of objects into a single object Lodash

Question

I have been trying to get this right and was having issues so figured i should ask ppl with more experience. I have an array of objects lets say called items, and I need to sum up some of the properties across different objects in the array and sum them up those at the end. The user can make a few selections and i need to only sum up the only the chosen properties in the array they give me so i thought maybe to use the _.pick function in lodash. If possible i would like to do that in one loop since the items array could have upto a 1000 items. Here is an example:

var items = [
{'lightBlue':4, 'darkBlue':2, 'red':4, 'orange':6, 'purple':7},
{'lightBlue':6, 'darkBlue':5, 'red':1, 'orange':2, 'purple':3},
{'lightBlue':2, 'darkBlue':4, 'red':3, 'orange':4, 'purple':9}
]

var userSelectedColors = ['lightBlue', 'darkBlue'];

What I want to see is all the blue's summed up like:

var summedUp = [{'lightBlue':12, 'darkBlue':11}];

Then sum up the results to get the total no

var totalCount = 23

Whats the best and performant way to get this in lodash. The array of userSelectedColors could be 1 or any combination of the colors.

Please provide an example, thanks your helps appreciated!

Unless items is very very large, performance likely won't be a concern. A non-lodash solution would probably be fastest. — castletheperson
– castletheperson, Commented Jul 19, 2016 at 2:43
Hi thanks @4castle can you provide an example of how to get the result i mentioned above? — Shokwave
– Shokwave, Commented Jul 19, 2016 at 2:45

castletheperson · Accepted Answer · 2016-07-19 05:22:59Z

23

Use _.sumBy

var totalCount = _.sumBy(userSelectedColors, _.partial(_.sumBy, items));

var items = [
  { 'lightBlue': 4, 'darkBlue': 2, 'red': 4, 'orange': 6, 'purple': 7 },
  { 'lightBlue': 6, 'darkBlue': 5, 'red': 1, 'orange': 2, 'purple': 3 },
  { 'lightBlue': 2, 'darkBlue': 4, 'red': 3, 'orange': 4, 'purple': 9 }
], userSelectedColors = ['lightBlue', 'darkBlue'];

var totalCount = _.sumBy(userSelectedColors, _.partial(_.sumBy, items));

console.log(totalCount);

<script src="https://cdn.jsdelivr.net/lodash/4.13.1/lodash.min.js"></script>

Expanded, that looks like:

var totalCount = _.sumBy(userSelectedColors, function(prop) {
    return _.sumBy(items, prop);
});

Without Lodash, a more performant solution would be something like this:

var totalCount = items.reduce(function(total, obj) {
    return total + userSelectedColors.reduce(function(total, prop) {
        return total + obj[prop];
    }, 0);
}, 0);

var items = [
  { 'lightBlue': 4, 'darkBlue': 2, 'red': 4, 'orange': 6, 'purple': 7 },
  { 'lightBlue': 6, 'darkBlue': 5, 'red': 1, 'orange': 2, 'purple': 3 },
  { 'lightBlue': 2, 'darkBlue': 4, 'red': 3, 'orange': 4, 'purple': 9 }
], userSelectedColors = ['lightBlue', 'darkBlue'];

var totalCount = items.reduce(function(total, obj) {
    return total + userSelectedColors.reduce(function(total, prop) {
        return total + obj[prop];
    }, 0);
}, 0);

console.log(totalCount);

<script src="https://cdn.jsdelivr.net/lodash/4.13.1/lodash.min.js"></script>

edited Jul 19, 2016 at 5:22

answered Jul 19, 2016 at 2:47

castletheperson

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10 Comments

user94559 Over a year ago

Actually, this doesn't give you access to the summary ({ lightBlue: 12, darkBlue: 13 }). Maybe I misunderstood the question?

castletheperson Over a year ago

@smarx Hmm, well the OP selected it, maybe they only really cared about the totalCount?

user94559 Over a year ago

@4castle I guess so. I've deleted my answer, but I can resurrect it if it turns out the summary is needed. :-)

Shokwave Over a year ago

Yes @smarx i was just trying to explain the process ultimately i wanted the aggregate sum.

castletheperson Over a year ago

@jamesemanon Sure. It's a functional programming technique I learned from Haskell. It's just a short way of saying to apply the first parameter of the callback to the second parameter of the nested _.sumBy. I've editted to show more of that.

|

user94559 · Accepted Answer · 2016-07-19 02:59:44Z

5

In terms of efficiency, I believe this is hard to beat, since it only iterates once through the array, but it's not quite as succinct as an approach like the one @4castle took. (Also, for only 1000 items, you're never going to notice the performance difference anyway.)

var items = [
    {'lightBlue':4, 'darkBlue':2, 'red':4, 'orange':6, 'purple':7},
    {'lightBlue':6, 'darkBlue':5, 'red':1, 'orange':2, 'purple':3},
    {'lightBlue':2, 'darkBlue':4, 'red':3, 'orange':4, 'purple':9}
]

var userSelectedColors = ['lightBlue', 'darkBlue'];

var sums = {};

_.each(items, function (item) {
    _.each(userSelectedColors, function (color) {
        sums[color] = (sums[color] || 0) + item[color];
    });
});

console.log('Summary: ', sums);

console.log('Grand total: ', _.sum(_.values(sums)));

Output:

Summary:  { lightBlue: 12, darkBlue: 11 }
Grand total:  23

answered Jul 19, 2016 at 2:59

user94559

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1 Comment

mikey Over a year ago

Awesome, thank you! I was looking for something without nested loops, (I have something similar, just using lodash forEach). Anyway thank you so much for helping me out!

firdaus hishamuddin · Accepted Answer · 2021-09-22 04:42:10Z

1

Getting the Summary

var summary = userSelectedColors.map(c => ({ [c]: _.sumBy(items, c)}))

Total

var total = _.sum(Object.values(summary))

edited Sep 22, 2021 at 4:42

answered Sep 22, 2021 at 4:29

firdaus hishamuddin

114 bronze badges

1 Comment

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