user1774309 - 9 months ago 29

Javascript Question

I need help to learn how to make a reduce to a array like this:

`a=[ ["ww","fsf",40],["ww","fsf",30],["ww","fsf",10]]`

I want to learn how to sum the 40+30+10 using the method reduce. I know how to do it if the array was [40,30,10].

Can anyone help me? Thank you.

Answer

`.reduce`

applies a function against an accumulator and each value of the array (from left-to-right) to reduce it to a single value:

```
a.reduce(callback[, initialValue])
```

Your values will be arrays:

```
["ww","fsf",40]
["ww","fsf",30]
["ww","fsf",10]
```

So you can use:

```
a.reduce(function(sum, value) {
return sum + value[2];
}, 0);
```

Or using ES6 new arrow functions:

```
a.reduce((sum, value) => sum + value[2], 0);
```