Problem sorting an array with sort()
One of these occurs when I want to sort a array of numbers.
Ex:
var a = [44,7,5,6,4,2,1];
a.sort();
console.log(a);
The expected result would be:
[1, 2, 4, 5, 6, 7, 44], but what is always returned to me is [1, 2, 4, 44, 5, 6, 7].
This is a very small array, but what I'm working on(with more than 300 occurrences) has happened the same. 115 appears before 2, for example.
3 answers
To order numbers you need to pass a comparison function to the method.
Test with
function(a, b) {
return a - b;
}
The Return of this function is what indicates to the method the position of the element relative to what is being compared.
I.e.:
var a = [44,7,5,6,4,2,1];
a = a.sort(function(a, b) {
return a - b;
});
console.log(a); // dá [1, 2, 4, 5, 6, 7, 44]
JsFiddle: https://jsfiddle.net/e3gx7dgv/1
As @Maniero indicated the comparison that the method does (without passing it a function) does not do what you think. the official specification is :
If comparefn is not undefined and is not a consistent comparison function for the elements of this array (see below), the behaviour of sort is implementation-defined.
That is, when a function is not passed what is done is at the discretion of browser . In MDN it is mentioned that the values will be treated as String and I think that is what the biggest stop of the browsers does. (read more at MDN in English here )
JavaScript treats the elements as string, so the "problem" happens. Solution:
var a = [44, 7, 5, 6, 4, 2, 1];
a.sort(function(a, b) { return a - b; });
console.log(a);You can do the following to sort correctly by passing a function of callback as a parameter to the function sort:
var a = [44,7,5,6,4,2,1];
a.sort(function(a, b) {
return a - b;
});
document.write(a);
//console.log(a);Or you could also do it this way:
var a = [44,7,5,6,4,2,1];
a.sort(function(a, b){
return a > b;
});
document.write(a);