2

Sorting multi-dimensional array in JavaScript. Perused other posts, but can't figure out how to pass the array members to the custom sort function, which determines whether to sort a string or numbers. Custom sort function is this:

function colSort(a, b) {
    if (sortDown) dValue = 1
    else dValue = -1;

    if (isNumeric(a[sortIndex])) {
        return (b[sortIndex] - a[sortIndex]) * dValue;
    } else {
        var astring = a[sortIndex].toLowerCase();
        var bstring = b[sortIndex].toLowerCase();
        if (bstring > astring) return -dValue;
        if (bstring < astring) return dValue;
        return 0;
    }
}

Array looks like this:

var qbStats =[

   ['David Lea', 'GB', 343, 502, 68.3, 4643, 9.2, 45, 6, 122.5],

   ['Kevin Whyte', 'NO', 440, 622, 70.7, 5087, 8.2, 41, 13, 108.4]

]

The column headers in a HTML table listing array members should be able to be clicked to sort ascending/descending on the clicked column.

I can't figure out how to indicate members to be sorted on the clicked index.

I know it starts as:

qbStats.sort(colSort(a,b));

But I don't know how to pass the array members to be sorted on the specific index. Ex: How do I tell it to sort on 'GB' and 'NO' as 'a' and 'b'? Thanks for any help you can give!

Improve this question
2
  • It's not clear exactly how you want the array(s) to be sorted. Can you give an example with three or four rows and explain how they should be ordered and why? Commented Jan 24, 2016 at 15:06
  • Wait - I think I get it. You want to order the whole list by the value of one column. OK. Commented Jan 24, 2016 at 15:07

2 Answers 2

Reset to default
1

The comparison callback to the sort() function is called by the sorting process and passed pairs of array elements. You don't have to tell anything which elements to compare; the sorting process already knows that.

In your case, the issue is that you essentially need a sort function per column. You can handle that by creating a function that returns another function, one that "knows" which column to compare:

function byColumn(sortIndex) {
  return function colSort(a, b) {
    if (sortDown) dValue = 1
    else dValue = -1;

    if (isNumeric(a[sortIndex])) {
      return (b[sortIndex] - a[sortIndex]) * dValue;
    } else {
      var astring = a[sortIndex].toLowerCase();
      var bstring = b[sortIndex].toLowerCase();
      if (bstring > astring) return -dValue;
      if (bstring < astring) return dValue;
      return 0;
    }
  };
}

And then:

qbStats.sort(byColumn(4)); // sort by column 4

The byColumn() function is just a simple wrapper around your comparator function. When it is called, it returns the actual function that the sort process will use. That function has access to the sortIndex parameter that was passed in at its creation time, so it intrinsically "knows" how to compare two rows.

Improve this answer
Sign up to request clarification or add additional context in comments.

3 Comments

I think this may be a little closer to what I need, but where do 'a' and 'b' come from? Aren't they the first dimension array items? How then does colSort know the index on which to sort? Is the script supposed to just "know" what a and b are?
The "a" and "b" parameters come from the sorting mechanism. The sort has to compare pairs of values from the array, and so to do that it calls your comparator function with two values. Your function does not need to worry about which two values they are; it just needs to respond with the answer to which one should come first.
I think I am starting to get it. What I did was just use array.sort(colSort);, and it did what you said, it "knew" to pull values a and b as the sort() command iterated through each set of compared items. I was making it harder than it needed to be, but your response helped me to see the solution.
0

Maybe this is something for you. The function returns for any case the right function to compare.

var qbStats = [['David Lea', 'GB', 343, 502, 68.3, 4643, 9.2, 45, 6, 122.5], ['Kevin Whyte', 'NO', 440, 622, 70.7, 5087, 8.2, 41, 13, 108.4]];

function sort(column, sortOrder, isNumber) {
    if (isNumber) {
        if (~sortOrder) {
            return function (a, b) {
                return a[column] - b[column];
            }
        } else {
            return function (a, b) {
                return b[column] - a[column];
            }
        }
    } else {
        if (~sortOrder) {
            return function (a, b) {
                return a[column].localeCompare(b[column]);
            }
        } else {
            return function (a, b) {
                return b[column].localeCompare(a[column]);
            }
        }
    }
}

qbStats.sort(sort(0, 1, false)); // sort 0th column, ascending by string
document.write('<pre>' + JSON.stringify(qbStats, 0, 4) + '</pre>');

qbStats.sort(sort(2, -1, true)); // sort 2th column, descending by number
document.write('<pre>' + JSON.stringify(qbStats, 0, 4) + '</pre>');

Improve this answer

1 Comment

I appreciate your response, but I'm still a little lost. The sort function will end up dynamically sorting any one of several arrays, so the arrays need to be passed in to the sort function dynamically, and the index on which to sort must also be passed in dynamically. I am also required to use the colSort() function, as described earlier.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.