Parse a string representing an array of floats

Question

I have a string as such:

string = "[x,y,z]"

Where x, y and z are valid javascript floats as strings. Some examples:

-0.9999
1.
1.00000000000E-5
-1E5

What is the most efficient (fastest) way to parse this string into an actual javascript array of floats without using Eval?

Now I do this:

parseFloatArray = function(string){
    // isolate string by removing square brackets
    string = string.substr( 1, string.length-2 )

    // create array with string split
    var array = string.split(',');

    // parse each element in array to a float
    for (var i = 0, il = array.length; i < il; i++){
        array[i] = parseFloat(array[i]);
    }

    // return the result
    return array
}

It is important that the solution works correctly for the above examples.

I also tried with JSON.parse which seemed perfect at first, but it returns a SyntaxError for the second example 1. where there is nothing following the decimal separator.

I prepared a fiddle for testing.

@zerkms I sort of agree, in that parseFloat will accept it, but in no number system can a decimal place exist without a numeric after it. This problem is XY - fix whatever is producing an invalid(ish) string representing an array (or make it return an array not a string, for that matter!). — Jamiec
– Jamiec, Commented May 27, 2016 at 8:52
1..toSource() is valid JS code where 1. is number and .toSource() is its method. — Radek Pech
– Radek Pech, Commented May 27, 2016 at 8:53
@Jamiec Yes, if you have method toSource() then it works. You can try other methods, e.g. 1..valueOf(). — Radek Pech
– Radek Pech, Commented May 27, 2016 at 8:59

Cyril Cherian · Accepted Answer · 2016-05-27 08:58:26Z

2

Instead of this

array[i] = parseFloat(array[i]);

try array[i] = +array[i];

Above handles all the test cases pretty well.

Here is the working fiddle

answered May 27, 2016 at 8:58

Cyril Cherian

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1 Comment

Wilt Over a year ago

Would be interesting to see some numbers on the performance of this compared to parseFloat and Number. jsPerf is down for some time already, I should maybe do it manually.

limekin · Accepted Answer · 2016-05-27 09:16:57Z

1

Try this :

str = "[-0.9999, 1., 1.00000000000E-5,-1E5]";
str.slice(1, str.length-1).split(',').map(Number);
// [-0.9999, 1, 0.00001, -100000]

edited May 27, 2016 at 9:16

answered May 27, 2016 at 9:11

limekin

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Comments

Nagoor Hussain Shaik · Accepted Answer · 2016-05-27 09:02:12Z

0

parseFloat basic syntax is parseFloat(string). https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/parseFloat

If you think the input values are only numbers you can use Number(x) rather than parseFloat.

Also, you might get different values upon parsing because all floating-point math is based on the IEEE [754] standard. so use toPrecision() method to customize your values- https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_objects/Number/toPrecision.

answered May 27, 2016 at 9:02

Nagoor Hussain Shaik

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Vishwa · Accepted Answer · 2016-05-27 09:26:11Z

0

Instead of you writing the for loop, you can always use the javascript built in array.prototypes

var string = "[1.,-0.9999,-1.00000E-5]";
var array = string.substr( 1, string.length-2 ).split(',');

console.log(array.map(function(i){return parseFloat(i);}));

you can also use the unary operator instead of parseFloat().

console.log(array.map(function(i){return +i;}));

answered May 27, 2016 at 9:26

Vishwa

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2 Comments

Wilt Over a year ago

I think array.map( parseFloat ); would be enough, you don't have to wrap it in a function.

Vishwa Over a year ago

Yes. That is the short form of what I wrote. Internally this is process array.map(function(i){return parseFloat(i);})

PRDeving · Accepted Answer · 2016-05-27 08:56:47Z

-1

Most efficient to extract is replacing and splitting.

var str = "[312.413,436.6546,34.1]"; // string

str = () => str.replace(/\[|\]/g, "").split(","); //[312.413, 4...] Array

most eficient to parse is just preceed the string with a "+", that will numerify it and, since javascript works with floats as primitives (and not integers), they will be automatically parsed.

var a = "1.00000000000E-5";
console.log( +a ); // 0.00001

edited May 27, 2016 at 8:56

answered May 27, 2016 at 8:50

PRDeving

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