JavaScript array not returning numbers

Question

When I use numbers in the example below, I get the correct return/output.

var array = [1,2,4,5,];
divBy2 = v => v / 2;
var result = array.map(divBy2);

When I try this below, I get NaV.

var array = [output];
divBy2 = v => v / 2;
var result = array.map(divBy2);

My code is written as below. Basically, I'm loading a text file with the following line:

Numbers (999.000,999.000),(999.000,999.000),

Then I want to create an array and take those numbers and divide by 2. To return just the numbers without the entire string.

var reader = new FileReader();

function readText(that){

        if(that.files && that.files[0]){
            var reader = new FileReader();
            reader.onload = function (e) {  
                var output=e.target.result;


output=output.split("\n").filter(/./.test,/Numbers/).join("\n").replace(/[^0-9.,]/g,'');

var array = [output];
divBy2 = v => v / 2;
var result = array.map(divBy2);

document.getElementById('inputTextToSave').innerHTML= output;

array=output; you dont want a nested array... also why do you join() if you want an array? — Jonas Wilms, May 06 '17 at 10:20
Is this some kind of assignment? http://stackoverflow.com/questions/43705581/javascript-use-an-array-to-calculate-some-coordinates/43705727 — Brett East, May 06 '17 at 10:23
Also don't put `array = [output]` using `[]` this will put your output array inside another array. — Brett East, May 06 '17 at 10:24

sabithpocker · Accepted Answer · 2017-05-06T11:03:09.810

You cannot place a string inside array to get the comma separated syntax work, it creates an array with a single string ("1,2,3") instead.

let output = "1,2,3";
var array = [output];//doesnt  work
//this creates  ["1,2,3"]
//array[0] === "1,2,3"
console.log("array", array);

var array2 = output.split(",");//works but creates string array
//this creates  ["1","2","3"]
//array2[0] === "1"
//array2[1] === "2"
//array2[2] === "3"
console.log("array2", array2)

var array3 = output.split(",").map(Number);//works and converts to number
//this creates  [1,2,3]
//array2[0] === 1
//array2[1] === 2
//array2[2] === 3
console.log("array3", array3)

//The closest to your attemp is eval() which shouldnt be used in normal cases
var array4 = eval("[" + output + "]");
console.log(array4)

output is a comma separated string in your code (999.000,999.000,999.000,999.000,999.000,999.000,999.000,999.000,999.000), split it into an array using String.prototype,split

let output = `Numbers (999.000,999.000),(999.000,999.000),
Numbers (999.000,999.000),(999.000,999.000),
Numbers (999.000,999.000),(999.000,999.000),
Numbers (999.000,999.000),(999.000,999.000)`;

output=output.split("\n").filter(/./.test,/Numbers/).join("\n").replace(/[^0-9.,]/g,'');
console.log(output);
let array = output.split(",");
console.log(array);
let divBy2 = v => v / 2;
let result = array.map(divBy2);
   console.log(result);

To take a look at your code:

let output = "1, 2, 3";
var array = [output];
console.log(array);//["1,2,3"]
divBy2 = v => v / 2;
var result = array.map(divBy2);
console.log(result);//[NaN]  as "1,2,3"/2 =NaN (not a number)

thanks a lot for your help... just one more question... my "output" return numbers with many decimal points.. i.e 3.77777,2.455555,83.2333. I only need 3 decimal points. Thanks — Alexa Atna, May 08 '17 at 07:04
@AlexaAtna You can use [`toFixed(3)`](http://stackoverflow.com/questions/11832914/round-to-at-most-2-decimal-places-only-if-necessary) which will return a string adjusted to 3 decimal places. in most cases. (**Note that approximations will not be perfect for all fractions, if you need more accuracy you will have to look into libraries implementing floating point arithmetic in a more precise way.**) — sabithpocker, May 08 '17 at 08:52

score 0 · Answer 2 · answered May 06 '17 at 10:27

There's small a mistake in your code.

output=output.split(............);

the above line of code will return you an array. So you could simply do this

var array = output;

or else you can define the variable at once

var array=output.split(............);

score 0 · Answer 3 · answered May 06 '17 at 10:27

You're likely getting an error because map is trying to apply itself to an array rather than a number.

Don't use array=[output]. If output is already an array, then you would get something like this [[3,5,656,34,23]], and the map function would then be trying to divide the entire inner array by 2, rather than each element.

array=output should do the trick, further, you could just map over output, like var result = output.map(divBy2);

JavaScript array not returning numbers

3 Answers3