Sorting Multidimensional Array

[kevinjacquier]

How do I set up a compare function (sorting arrays) for a multi-dimensional array when I want the sort to be based on the first 2 elements of the array.

If I have the array
3,Kevin
3,Alice
2,Steve
1,Adam
2,Sammy

I want to sort it so I get
1,Adam
2,Sammy
2,Steve
3,Alice
3,Kevin


array.sort(compareFunction)

function compareFunction(???)
{ ???? }


Any Help in the Compare Function would be appreciated. Or if there is a better approach.
I am only concerned with IE 4.0+

[voicebox]

Hi Kevin,

You should write a function that accepts two arguments (a and b) and should return something less than 0 if a < b, 0 if a == b or something greater than 0 if a > b . So you should write something comparing a[0] and b[0] and if they are equal compare a[1] and b[1].

[kevinjacquier]

I think I understand, Thanks

[Herb]

Hi,

I did something that will do the job:

function compare ( left, right ) {
    
    if ( left[0] < right[0] )
	return 1;
    else if ( left[0] > right[0] )
	return -1;
    else if ( left[1] < right[1] )
	return 1;
    else if ( left[1] > right[1] )
	return -1;
    else
	return 0;
    
}


function qsort ( array, lo, hi ) {

  var low  = lo;
  var high = hi;
  mid = array[ Math.floor( (low+high)/2 ) ];

  do {
    while ( compare(array[low],  mid) > 0 )
      low++;

    while ( compare(array[high], mid) < 0 )
      high--;

    if ( low <= high ) {
      swap( array, low, high );
      low++;
      high--;
    }

  } while ( low <= high );

  if ( high > lo )
    qsort( array, lo, high );

  if ( low < hi )
    qsort( array, low, hi );

}

function swap ( a, i, j ) {

  var tmp = a[i]; 
  a[i] = a[j];
  a[j] = tmp;

}


var array = new Array();

array[0] = new Array ( 3, "Kevin" );
array[1] = new Array ( 3, "Alice" );
array[2] = new Array ( 2, "Steve" );
array[3] = new Array ( 1, "Adam"  );
array[4] = new Array ( 2, "Sammy" );

qsort ( array, 0, array.length-1 );

It uses an adapted version of quicksort, the fastest sorting algorithm.

See the results at http://www.iro.umontreal.ca/~saintamh/test/sort

[Vincent Puglia]

Hi theScum

mon dieu, c'est manifique!

Only took a glance, but she does shine.

Vinny

[Herb]

mon dieu, c'est manifique!

hahahahaha

merci

[Vincent Puglia]

hi theScum,

laughing at my french ?

post it in the "Post a Javascript" section with some explanation.

thanks
Vinny

[Herb]

Hi Vinny and others,

I was not laughing at your french, it's just that the sentence was maybe a bit exaggerated

I wrote the explanations, and also improved the script so that it can sort arrays with more than 2 columns. Check it out.

ciao,
Scum

[Herb]

I just fixed a bug in the code that would make an error if two rows were equal.

I also added simplified instructions for those who want to use it but are not interested in how it works...