javascript sorting an array of strings

Question

I am having seemingly inconsistent results trying to sort arrays of strings using the sort method, both with and without passing sort() a function:

function sortThese(strArr) { 

    var words = [];
    for (var i = 0; i < strArr.length; i++) {
        words.push(String(strArr[i].length + "," + strArr[i]));
    }

    words = words.sort();
    console.log(words);
}

sortThese(["battt","catt","mat"]);
sortThese(["as","assssvvvvt","affggg"]);

in this case my results are:

["3,mat", "4,catt", "5,battt"]
["10,assssvvvvt", "2,as", "6,affggg"]

so it appears that the method is seeing my "10" as "1."

How do I make it see the value as 10?

Futher, if I pass sort this function:

words = words.sort(function(a,b){
    return a - b;
});

the result is not sorted:

["4,catt", "5,battt", "3,mat"]
["2,as", "10,assssvvvvt", "6,affggg"]

I would love some clarification regarding how I should expect the sort method to behave, and how to make it sort these strings! Thank you

Answer 1

The "10" comes before "3", because you've made it into a string (ie, "1" comes before "3"). If you want to sort by length, you could use the sort function to compare lengths:

words.sort(function(a, b) { return a.length > b.length; });

Fiddle

You could also create a nested object array, in order to hold a number and the string in each item:

var words = strArr.map(function(str) { 
    return { len: str.length, str: str } 
});
words.sort(function(a, b) { return a.len > b.len; });

(Of course, this second approach is unnecessary for the example case, but may be useful in other cases.)

Fiddle

Answer 2

Sorting strings always uses alphabetical order, not numerical. Just imagine 0=A 1=B 2=C and so on. Letters are not connected as numbers, so everything starting with 1 (respective B) will be sorted before 2 (respective C). That's why you get 10,2,6. For 10, only the 1 counts.

Using a custom sort function is a good way to achieve this. But you cannot subtract strings. Extract the integer before and compare afterwards:

words = words.sort(function(a,b){
    //parseInt will read only the first numbers and discard the letters after this
    return parseInt(a) - parseInt(b) 
});