dc.js - how to get the average of a column in data set

Question

I have this below data.

col1    col2    value
a   01/01/14    10
a   01/01/14    35
a   01/01/14    68
a   01/01/14    21
a   01/01/14    24
b   01/01/14    26
b   01/01/14    35
b   01/01/14    39
b   01/01/14    87
c   01/01/14    25
c   01/01/14    63
c   01/01/14    11
c   01/01/14    25
c   01/01/14    35

If I wanted to take the sum of col1. I could do it by using col1Dim.group().reduceSum(function(d) { return d.value }). If I need the count i can replace sum with count.

But I'm here loooking for average. So to that. I need to take sum of col1 and count of col1.

Any idea how can i divide and get the average?

Please help. Stuck in this for almost 3 days.

Answer 1

You need to use the group.reduce(add, remove, initial) method, like:

var col1DimTotal = col1Dim.group().reduce(reduceAdd, reduceRemove, reduceInitial);

function reduceAdd(p, v) {
  ++p.count;
  p.total += v.value;
  return p;
}

function reduceRemove(p, v) {
  --p.count;
  p.total -= v.value;
  return p;
}

function reduceInitial() {
  return {count: 0, total: 0};
}

Because you're using dc.js, you'll need to use chart.valueAccessor method to use the average in your charts, like:

chart.valueAccessor(function(p) { return p.value.count > 0 ? p.value.total / p.value.count : 0; });