Say I have an array-ish container of decimal numbers. I want the sum. In Python I would do this:
x = [1.2, 3.4, 5.6]
sum(x)
Is there a similarly concise way to do this in JavaScript?
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2 Answers
Another approach, a simple iterative function:
function sum(arr) {
var result = 0, n = arr.length || 0; //may use >>> 0 to ensure length is Uint32
while(n--) {
result += +arr[n]; // unary operator to ensure ToNumber conversion
}
return result;
}
var x = [1.2, 3.4, 5.6];
sum(x); // 10.2
Yet another approach using Array.prototype.reduce:
var arr = [1.2, 3.4, 5.6];
arr.reduce(function (a, b) { return a + b; }, 0); // 10.2
The reduce method is part of the ECMAScript 5th Edition standard, is widely available, but is not on IE <= 8, however an implementation cay be included from the the Mozilla Dev Center I linked.
answered Jul 30, 2010 at 2:04
Christian C. Salvadó
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Comments
I guess there's none... but you can make one on javascript
Array.prototype.sum = function() {
return (! this.length) ? 0 : this.slice(1).sum() +
((typeof this[0] == 'number') ? this[0] : 0);
};
use it as,
[1,2,3,4,5].sum() //--> returns 15
[1,2,'',3,''].sum() //--> returns 6
[].sum() //--> returns 0
x = [1.2, 3.4, 5.6]
x.sum(); // returns 10.2
demo
Okay as pointed out in the comment, you can also do it as non-recursive way
Array.prototype.sum = function() {
var num = 0;
for (var i = 0; i < this.length; i++) {
num += (typeof this[i] == 'number') ? this[i] : 0;
}
return num;
};
Another way to do it, through function..
function sum(arr) {
var num = 0;
for (var i = 0; i < arr.length; i++) {
num += (typeof arr[i] == 'number') ? arr[i] : 0;
}
return num;
};
use it as,
sum([1,2,3,4,5]) //--> returns 15
x = [1.2, 3.4, 5.6]
sum(x); // returns 10.2
8 Comments
catchmeifyoutry
just out of curiosity, wouldn't this recursive implementation easily hit the stack limit? Any reason not to use an iterative solution with a for loop?
Stefan Kendall
This is a terrible solution. Please do not go modifying object prototypes. I've run into serious issues with this kind of nonsense. Write a $.sum jQuery plugin, and don't screw the rest of us.
Reigel Gallarde
@Stefan Kendall can you give me something to read or any for that matter?
modifying object prototypes... ;)
Alex Martelli
@Stefan, wish I could +1000 you -- the ability to modify built-ins is one detail I classify as a defect in JS (and Ruby) and it has never given me anything but trouble (esp. in JS as I don't use Ruby much;-).
Christian C. Salvadó
@Reigel: Give a look to this article.
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