Sort By Multiple Dimensions In Crossfilter.js

I'm using Mike Bostock's crossfilter library to filter and sort large datasets. My problem: Given a dataset with multiple dimensions, how can I sort on more than one dimension at a

Solution 1:

I know it's not using the crossfilter library, but why not use the sort function to do this?

var combos = cf.sort(function(a,b) { 
   if(a.cat == b.cat) return a.val < b.val ? -1 : 1;
   return a.cat < b.cat ? -1 : 1;
});

see http://jsfiddle.net/cQXNK/5/

To allow different dimensions to have different sort directions would just be a matter of swapping -1 for 1 and vice versa

Solution 2:

Using the Array.prototype.sort, you can:

functionsortByPriority(a, b) {
    var p = sortByPriority.properties;
    functionpad(str, max) {
        str = String(str);
        return str.length < max ? pad("0" + str, max) : str;
    }

    if (!p) {
        return a - b;
    }
    var ar ='', br = '';
    for (var i = 0, max = p.length; i < max; i++) {
        ar += pad(a[p[i]], 10);
        br += pad(b[p[i]], 10);
    }
    return ar == br ? 0 : ar > br ? 1 : - 1;
}

How to use:

Sorting cat then val

sortByPriority.properties = ['cat', 'val'];
myArray.sort(sortByPriority);

Result:

• A 1
• A 3
• A 11
• A 11
• B 2
• B 2
• B 5
• B 100

if you want prior val do:

sortByPriority.properties = ['val', 'cat'];
myArray.sort(sortByPriority);

Result:

• A 1
• B 2
• B 2
• A 3
• B 5
• A 11
• A 11
• B 100

Not a super effective code but, you can improve it.

UPDATE:

You can use the pad function to get same results using crossfilter, look this jsfiddle.

var combos = cf.dimension(function(d) { 
    returnpad(d.cat, 10) + '|' + pad(d.val, 10); 
});

You also can change the pad size by the same length from the biggest string in your "coll", this will ensure the result ever.

See that optimization: http://jsfiddle.net/gartz/cQXNK/7/

Solution 3:

Here's what I ended up doing:

• I still use string concatenation on a single new dimension, but

• I convert the measure to a positive, comparable decimal before turning it into a string, using crossfilter to get the min/max:

  var vals = cf.dimension(function(d) { return d.val }),
      min = vals.bottom(1)[0].val,
      offset =  min < 0 ? Math.abs(min) : 0,
      max = vals.top(1)[0].val + offset,
      valAccessor = function(d) {
          // offset ensures positive numbers, fraction ensures sort order
          return ((d.val + offset) / max).toFixed(8);
      },
      combos = cf.dimension(function(d) { 
          return d.cat + '|' + valAccessor(d); 
      });
  

See working fiddle: http://jsfiddle.net/nrabinowitz/cQXNK/9/

This has the advantage of handling negative numbers properly - not possible with zero-padding, as far as I can tell. It seems to be just as fast. The downside is that it requires creating a new dimension on the numeric column, but in my case I usually require that in any case.

Solution 4:

I haven't tested for preformance but you could give d3.nest a go. Example code:

var nested = d3.nest()
.key(function(d) { return d.cat; })
.sortKeys(d3.ascending)
.sortValues(compareValues)
.entries(data);

See the whole fiddle here: http://jsfiddle.net/RFontana/bZX7Q/

And let me know what result you get if you run some jsperf :)