Negative Barchart with Androidplot

Question

I'm using the Androidplot library to plot a Barchart to display something. The range of my values are -40 till +40.

How can I plot a bar to the negative side? I just want to center the zero on the y-axis in the middle and the bars should growing up or down, if the value is positiv of negativ. My bars are growing from the lower bound upwards. It should look like this:

Answer 1

That works for me:

plot.centerOnRangeOrigin(0);

plot.setRangeLowerBoundary(0,BoundaryMode.AUTO);

Where plot is a instance of XYPlot.

Answer 2

Negative bar support has recently been added to Androidplot 0.6.2; you'll need to use the latest development version to get it (it's very stable).

Once you have the correct version of Androidplot you can use Maria Reina's suggestion to enable the display of negative values. Here's how I'm doing it in the screenshot below:

plot.setUserRangeOrigin(0);
plot.setRangeBoundaries(0, BoundaryMode.AUTO, 0,BoundaryMode.AUTO);

Note : There is currently a bug where if you are using overlay mode with 2 or more series and have negative bars, the overlay order of negative bars is reversed, causing the smaller negative values in a bargroup to be obscured by the larger ones. If your goal is simply to reproduce the image above though then you should be fine.

Answer 3

That's a great question. I think there's no way to do that with the current version of AndroidPlot (0.6.0) with a single series of values. I created a workaround in my project. I know it's not perfect, but it works: create two series that overlap, one in green and one in the background color. Suppose you have your currentValue to draw..

if (currentValue>=0) {
    greenRes[i] = Float.valueOf(currentValue);
    coverRes[i] = Float.valueOf(0);
}
else {
    greenRes[i] = Float.valueOf(0);
    coverRes[i] = Float.valueOf(currentValue);
}

In this way you always have the green bar starting from the zero axis and going up or down.