How do I create a new scale() function in d3.js? I would like to create a cumulative distribution function

Question

How do I create my own scale() function in d3?

I am trying to replace the nice linear scale in d3 d3.scale.linear() with a different function that I would like to create myself. My new scale would be based on a cumulative distribution function, so that the median value would appear in the center of the x axis, and a value that was two standard deviations from the median would appear twice as far from the center of the x axis as something that was one standard deviation from the mean.

Here is a link to my jsfiddle page: http://jsfiddle.net/tbcholla/kR2PS/3/ (I would appreciate any other comments you might have about my code as well!)

right now I have:

var x = d3.scale.linear()
.range([0, width])
.domain(d3.extent([0, data.length]));    

I've seen scale.pow() and scale.log(). Now I'd like to create a new function! Thanks! EDIT: I found the function scale.quantile(), which might hold the solution for me. My related question: Plotting a line graph with scale.quantile()

Answer 1

This is an example how we can add new functionality in d3.scale.liner(). For null values my function returns null (d3.scale.liner() returns 0 in this case). The primary approach is to wrap the original scale and all his methods.

I didn't test this function for all cases. But for basic functionality it's working. Unfortunately I didn't found easier way to do it :(

/**
 * d3.scale.linear() retrun 0 for null value
 * I need to get null in this case
 * This is a wrapper for d3.scale.linear()
 */
_getLinearScaleWithNull: function() {
    var alternativeScale = function(origLineScale) {
        var origScale = origLineScale ? origLineScale : d3.scale.linear();

        function scale(x) {
            if (x === null) return null; //this is the implementation of new behaviour
            return origScale(x);
        }

        scale.domain = function(x) {
            if (!arguments.length) return origScale.domain();
            origScale.domain(x);
            return scale;
        }

        scale.range = function(x) {
            if (!arguments.length) return origScale.range();
            origScale.range(x);
            return scale;
        }

        scale.copy = function() {
            return alternativeScale(origScale.copy());
        }

        scale.invert = function(x) {
            return origScale.invert(x);
        }

        scale.nice = function(m) {
            origScale = origScale.nice(m);
            return scale;
        }

        scale.ticks = function(m) {
            return origScale.ticks(m);
        };


        scale.tickFormat = function(m, Format) {
            return origScale.tickFormat(m, Format);
        }

        return scale;
    }

    return alternativeScale();
},