sumBy returns bool instead of integer when the result equals 1

[JonWallsten]

I've noticed that sumBy in Lodash 4 returns bool true instead of 1 if the sum is 1. If the sum is 2 or more it returns an integer as usual. Is this expected behavior?

[jdalton]

_.sumBy([{ 'x': 1 }], 'x')
// 1

[JonWallsten]

//list.items
//[{isNew: true}]
list.newItemCount = _.sumBy(list.items, {isNew: true});
//true

//list.items
//[{isNew: true}, {isNew: true}]
//list.newItemCount = _.sumBy(list.items, {isNew: true});
//2

[jdalton]

See. next time, lead with an example :P

You're using the iteratee a bit odd by using the matches shorthand as it will produce a boolean which is what will be used to compute the sum.

true + true // 2

[JonWallsten]

That's a weird behavior for "sum". So how do I count the number of occurrences of isNew: true in one line? I mean, this code was working until I updated to Lodash 4.

Edit: _.sumBy(list.items, 'isNew'); returns the same thing. So the problem is that 'isNew' is a bool?

[JonWallsten]

_.countBy(list.items, 'isNew')['true']; // seems a bit ugly?

[jdalton]

So the problem is that 'isNew' is a bool?

Yeah, though you could do

_.sumBy(list.items, _.flow(_.property('isNew'), Number));

or

_.countBy(list.items, 'isNew')['true']; // seems a bit ugly?

Naw, it's great. I was just going to suggest it. It's also better suited for the given task.

[JonWallsten]

Cool, I guess I have to live with that from now on.

[thadd]

Why is this closed as invalid? This is really counter-intuitive behavior. I can't see any reason why sumBy should ever return anything except for a number.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.