Converting array of strings into numbers

Question

I'm trying to convert this array of strings (which are all integers) into an array of numbers. For some reason when I use the following function it doesn't change the first string in the array to a number. I'm not sure why. Can someone explain that to me?

var listArray = ['7', '4', '2', '12', '9'];
function makeNums(){
  for(var i = 0; i < listArray.length; i++){
    listArray[i] = parseInt(listArray[i], 10);
    listArray.sort(function(a,b) { return a - b; });
    console.log(listArray[i]);  
  }

}

makeNums();

Sort AFTER you turn the strings into integers Not DURING the conversion. It's trying to sort strings and numbers right now :( It moves the strings around so that you can't convert all of them to integers. — ahitt6345
– ahitt6345, Commented Oct 1, 2016 at 21:10
Why don't you just do listArray.map(function(num){ return 1*num}).sort(function(a,b) { return a - b; }) — androidavid
– androidavid, Commented Oct 1, 2016 at 21:14

Nina Scholz · Accepted Answer · 2016-10-01 21:14:45Z

4

You could convert it to number with Number as callback, then sort.

var listArray = ['7', '4', '2', '12', '9'].map(Number);
console.log(listArray);
listArray.sort(function (a,b) { return a-b; });
console.log(listArray);

Or you can first sort, because of the implicit casting to number and then convert the items to number.

var listArray = ['7', '4', '2', '12', '9'];
listArray.sort(function (a,b) { return a-b; });
console.log(listArray);
listArray = listArray.map(Number);
console.log(listArray);

answered Oct 1, 2016 at 21:14

Nina Scholz

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1 Comment

Alex Marple Over a year ago

This worked in the console but didn't jive with the rest of the problem I'm working on. This is a great answer though. Thank you Nina!

Sᴀᴍ Onᴇᴌᴀ · Accepted Answer · 2016-10-01 21:12:11Z

2

Move the sorting outside of the iteration. That way it won't sort until the array has been processed. Try running the code snippet below:

var listArray = ['7', '4', '2', '12', '9'];
function makeNums(){
  for(var i = 0; i < listArray.length; i++){
    listArray[i] = parseInt(listArray[i], 10); 
  }
  listArray.sort(function(a,b) { return a - b; });
  console.log(listArray); 
}

makeNums();

answered Oct 1, 2016 at 21:12

Sᴀᴍ Onᴇᴌᴀ

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1 Comment

Alex Marple Over a year ago

I can't use the map method and this answer did what I needed for a larger problem I'm working on. Thanks for the illumination!

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