Using an ordinal scale ('d3.scale.ordinal'

I have a data array like this:

var data = [{"Alphabet_Type":"a"}, {"Alphabet_Type":"b"}, {"Alphabet_Type":"a"}];

I am using:

dc.js
crossfilter.js
d3.js

I want to create a bar chart with:

the x-axis having an alphabet name, and
the y-axis having number of occurrences of the alphabet.

Question: How can I plot a bar chart with an ordinal scale on the x-axis?

My code:

var data = [{"Alphabet_Type":"a"}, {"Alphabet_Type":"b"}, {"Alphabet_Type":"a"}];

var Filter = crossfilter(data);
var Dimension = Filter.dimension(function (d) { return d.Alphabet_Type; });
var Group = Dimension.group();

dc.barChart("#bar-chart")
    .width(800) 
    .height(275) 
    .transitionDuration(0) 
    .margins({ top: 10, right: 50, bottom: 30, left: 40 })
    .dimension(Dimension) 
    .group(Group) 
    .elasticY(false)
    .elasticX(false)
    .x(d3.scale.linear().domain([-1, 10]))
    .y(d3.scale.linear().domain([0, 5]))
    .centerBar(true)
    .renderHorizontalGridLines(true)
    .renderVerticalGridLines(true)
    .brushOn(false);

Finally, I have another problem which is that Alphabet_Type is not going to have predictable values. So I need to fetch the values for Alphabet_Type via crossfilter.js and incorporate those values into the domain. How can I do this?

回答1:

Two things:

Pass dc.units.ordinal as the parameter to .xUnits().
Pass an ordinal scale function to .x().

Here's what I mean:

.x(d3.scale.ordinal().domain(["", "a", "b", "c"])) // Need empty val to offset first value
.xUnits(dc.units.ordinal) // Tell dc.js that we're using an ordinal x-axis

See this JSFiddle: http://jsfiddle.net/reblace/tbamW/156/

For some reason, I couldn't get renderHorizontalGridLines() or renderVerticalGridLines() to work, but the rest is good.

回答2:

Adding

.x(d3.scale.ordinal().domain(data.map(function (d) {return d.Alphabet_Type; })))

solved the problem.