CrossFilter (reduceSum) and negative numbers about crossfilter HOT 6 CLOSED

I'm having a hard time grokking the problem. Could you come up with something that doesn't use d3 (only crossfilter) and shows some numbers rather than bars? That might help identify the problem.

from crossfilter.

hey there, I think i narrowed it down, the problem isnt with reduceSum

its to do with the y.domain([-100, group.top(1)[0].value]);

which shows the key and value of the largest in the group
This works fine when all values in the y axis are positive:

however when you have negative values the largest number is the smallest negative.

The reason why the bars are exceeding the 0-100 y range is that the maximum value is based on an incorrect figure (of -90, when it should be based on -300)

i wonder if it would be possible to create another function - that would return the top array sorted with absolute values

y.domain([0, group.topAbs(1)[0].value]);

I believe that using absolute values would solve this issue

from crossfilter.

I think i solved it, but dont know what the effects will be on the rest of the crossfilter plugin

http://www.pixeltradr.com/crossfilter/indexPaymentsCrossfilter.html
http://www.pixeltradr.com/crossfilter/indexPaymentsCrossfilterNegative.html
http://www.pixeltradr.com/crossfilter/indexPaymentsCrossfilterPositive.html

Ive changed the crossfilter plugin in function heapselect() to include Math.abs() in three places:

Also edited the html file itself and added Math.abs() to:

y.domain([0, Math.abs(group.top(1)[0].value)]);

and in function barPath(group)

I think it would probably be better to create new functions like - function heapselectAbs(a, lo, hi, k) {}
for example to to handle this situation.

from crossfilter.

Decided to leave the old sort functions alone, and create new ones to handle this situation:

instead of:
y.domain([0, group.top(1)[0].value]);
its now
y.domain([0, group.topAbs(1)[0].value]);

New crossfilter file:
http://pixeltradr.com/crossfilter/crossfilter.v1.abs.js

changes:

• function topAbs(k)
• function heapselectAbs_by(f)
  ----- function heapselectAbs(a, lo, hi, k)

http://pixeltradr.com/crossfilter/crossfilter.v1.abs.js

from crossfilter.

I think the result you're looking for is entirely achievable via the existing API. The easiest way I can think of is to order the group by the absolute value of the sum.

var data = [ { key : 1, value : 1 }, { key : 2, value : -2 }, { key : 3, value : 3 }, { key : 4, value : -4 } ]
var cf = crossfilter(data);
var key = cf.dimension(function(d) { return d.key });

var group = key.group().order(function(p) { return Math.abs(p) });
group.reduceSum(function(d) { return d.value });
group.top(2);

// producing
[ { key: 4, value: -4 },
  { key: 3, value: 3 } ]

It also possible to use group.reduce() to write your own reduction that finds the absolute value directly (and you wouldn't need to change the ordering).

from crossfilter.

Wow thats awesome!
It works, Thanks alot!

from crossfilter.