Crazy Bug in setDomainValueFormat - androidplot

Question

I changed the sample code SimpleXYPlotActivity to format a domain label like this:
// create a couple arrays of y-values to plot:
Number[] domainLabels = {1, 2, 3, 6, 7, 8, 9, 10, 13, 14};
Number[] series1Numbers = {1, 4, 2, 8, 4, 16, 8, 32, 16, 64};
Number[] series2Numbers = {5, 2, 10, 5, 20, 10, 40, 20, 80, 40};
// turn the above arrays into XYSeries':
// (Y_VALS_ONLY means use the element index as the x value)
//XYSeries series1 = new SimpleXYSeries(Arrays.asList(series1Numbers), SimpleXYSeries.ArrayFormat.Y_VALS_ONLY, "Series1");
XYSeries series1 = new SimpleXYSeries(Arrays.asList(domainLabels), Arrays.asList(series1Numbers), "Series1");
//XYSeries series2 = new SimpleXYSeries(Arrays.asList(series2Numbers), SimpleXYSeries.ArrayFormat.Y_VALS_ONLY, "Series2");
XYSeries series2 = new SimpleXYSeries(Arrays.asList(domainLabels), Arrays.asList(series2Numbers), "Series2");
//...other lines
plot.setDomainValueFormat(new Format() {
#Override
public StringBuffer format(Object obj, StringBuffer toAppendTo, FieldPosition pos) {
int day = ((Number) obj).intValue();
System.out.println(day);
return new StringBuffer(day);
}
#Override
public Object parseObject(String source, ParsePosition pos) {
return null;
}
});
// reduce the number of range labels
//plot.setTicksPerRangeLabel(3);
// rotate domain labels 45 degrees to make them more compact horizontally:
plot.getGraphWidget().setDomainLabelOrientation(-45);
I dont know why, but plot print the following domain labels:
1, 2, 3, 5, 6, 8, 9, 11, 12, 13
and not the right values...
1, 2, 3, 6, 7, 8, 9, 10, 13, 14
Why has it this crazy behaviour?

Answer 1

Well to start, when I run the above code, no labels are printed at all. But if I replace:
return new StringBuffer(day);
with:
return toAppendTo.append(day);
Then the labels appear. Moving on...
Your formatter is truncating the floating point x-val associated with each domain tick label. The reason you have this floating point component is because you are specifying your own xVals when you instantiate SimpleXYSeries. I suspect that what you really want is to specify iVals only, since you dont actually create xVals anywhere.
I made these changes:
First, create your XYSeries instances to create xVals from iVals like this:
XYSeries series1 = new SimpleXYSeries(Arrays.asList(series1Numbers), SimpleXYSeries.ArrayFormat.Y_VALS_ONLY, "Series1");
XYSeries series2 = new SimpleXYSeries(Arrays.asList(series2Numbers),SimpleXYSeries.ArrayFormat.Y_VALS_ONLY, "Series2");
Next, update your domain formatter to use your domain label lookup array like this:
plot.setDomainValueFormat(new Format() {
#Override
public StringBuffer format(Object obj, StringBuffer toAppendTo, FieldPosition pos) {
int i = Math.round(((Number) obj).floatValue());
return toAppendTo.append(domainLabels[i]);
}
#Override
public Object parseObject(String source, ParsePosition pos) {
return null;
}
});
For anyone wondering why obj is first converted to a float and then rounded to an int before being used as an iVal: This is necessary to avoid the natural flooring behavior that occurs when converting float values to int values. If for example you were to call intValue on a Double representation of 1, you'd get 0 because internally it's represented as 0.99999999... and gets floored to 0 by the conversion instead of being rounded up to 1.