如何使用d3.js避免图中的log 0

Question

I am current working on library d3.js.I have line graph using Dynamic Line Graph Here we have option of drawing power linear and log. But my problem is that I might have some values zero in my data set and as log 0 is undefined so the code is unable to plot it. Here in my code the scale set like this

y = d3.scale.log().domain([0.1, max_y _value]).range([h, 0]).nice();

and this is how it is used

  lineFunction = d3.svg.line()
        .y(function(d) {
          return y(d);
        });

I know that its an odd question.But is there a way by which I can handle log 0 value so that if I have single zero value the rest of them are plotted correctly. Can I gave two domain and range in same statement (to handle 0 value) if yes than how will it bind to y axis?

Thanks any help will be appreciated.

Answer 1

I solved my problem by using a clamp function. This is how I have changed the code:

y = d3.scale.log().clamp(true).domain([0.1, max_y _value]).range([h, 0]).nice();

Answer 2

If you have a domain which has one of the domain boundaries as 0 log scale won't work for you. Also log scale provides you a tick() function with uncofigurable number of ticks.

My current assignment is to display data with arbitrary domains and ranges on a linear scaled scatter chart BUT optionally the user can change over to logarithmic scale. This includes the problematic [0,n] and [n,0] domains.

Here's a solution i came up with to handle these cases: The issue can be avoided if we are using a linear scale to project our domain to an arbitrary range with positive boundaries. I choose [1,10] but it can take any positive numbers. After that we can use a normal log scale.

d3.scale.genericLog = function() {
    return GenericLog();
};
function GenericLog() {
    var PROJECTION=[1,10];
    var linearScale, logScale;

    linearScale=d3.scale.linear();
    linearScale.range(PROJECTION);

    logScale=d3.scale.log();
    logScale.domain(PROJECTION);

    function scale(x) {
        return logScale(linearScale(x));
    }
    scale.domain = function(x) {
        if (!arguments.length) return linearScale.domain();
        linearScale.domain(x);
        return scale;
    };
    scale.range = function(x) {
        if (!arguments.length) return logScale.range();
        logScale.range(x);
        return scale;
    };
    scale.ticks = function(m) {
        return linearScale.ticks(m);
    };
    return scale;

}

Usage:

var scale1 = d3.scale.genericLog().domain([0,1]).range([500,1000]);
var scale2 = d3.scale.genericLog().domain([-10,0]).range([500,1000]);
scale1(0)   //500
scale2(-10) //500
scale2(0)   //100

I only needed the range(), scale(), ticks() functions so i only included these but it shouldn't take more than 5 minutes to implement all the others. Also: note that i was using the linear scale's ticks() values because I had to limit the number of ticks and that is easier with the linear scale.

EDIT: BE AWARE Depending on what you choose as PROJECTION it will distort your log scale. The wider interval you use will strecth your scale's lower part more.