How do I convert strings in an array to numbers using forEach?

Question

I am trying to sum the contents of an array like these:

var cardsBen = [10,2]

var cardsAmy = [4,10]

When I use a for loop, it works.

for(var i = 0; i < cardsBen.length; i++){
  cardsBen[i] = Number(cardsBen[i]);
}

When I use forEach, it doesn't convert.

cardsAmy.forEach(function(item)
  {
    Number(item);
  });

I know this because, when I then reduce the arrays, I get 12 for Ben and 410 for Amy.

var sumBen = cardsBen.reduce(function(sum, nbr){return sum + nbr});
var sumAmy = cardsAmy.reduce(function(sum, nbr){return sum + nbr});

What exactly do you think happens to the result of Number(item)? — jonrsharpe
– jonrsharpe, Commented Dec 1, 2017 at 21:24

ibrahim mahrir · Accepted Answer · 2017-12-01 21:53:39Z

7

Primitive values can't be mutated. So when doing Number(item) you have to assign that back to the array like:

cardsAmy.forEach(function(item, i) {
    cardsAmy[i] = Number(item);
});

And you can do that directly in reduce (without needing the above forEach code) like:

var sumBen = cardsBen.reduce(function(sum, nbr) { return sum + Number(nbr); }, 0);
//                                                             ^^^^^^^   ^

edited Dec 1, 2017 at 21:53

answered Dec 1, 2017 at 21:25

ibrahim mahrir

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5 Comments

Janet Over a year ago

Yes - That's it. Thanks. Can't click the check mark for 3 minutes.

RaphaMex Over a year ago

Best response would include an initial value to reduce. Try again with var cardsBen = [] and see,,,

ibrahim mahrir Over a year ago

@RaphaMex Good point! Added an initial value. Although I don't think it will be necessary (in this case).

Janet Over a year ago

At this point, I am just trying to learn how to use all the array methods instead of always using a for loop. I have searched for array katas on CodeWars to try to get some practice. I think a "next step" would be to learn to combine/string methods together. But, first things first.

ibrahim mahrir Over a year ago

@Janet Combining/chaining them will come natural once you understand them well. Good luck!

Nina Scholz · Accepted Answer · 2017-12-01 21:26:57Z

2

You could use reduce with an implicit casting to number with an unary plus +.

sum = array.reduce(function (s, v) {
    return s + +v;
}, 0);

answered Dec 1, 2017 at 21:26

Nina Scholz

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