Computes a reasonable set of labels for a data interval and number of labels.
/**
* Copyright (C) 2009, 2010 SC 4ViewSoft SRL
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
//package org.achartengine.util;
import java.text.NumberFormat;
import java.text.ParseException;
import java.util.ArrayList;
import java.util.List;
public class Util {
/** A value that is used a null value. */
public static final double NULL_VALUE = Double.MAX_VALUE;
/**
* A number formatter to be used to make sure we have a maximum number of
* fraction digits in the labels.
*/
private static final NumberFormat FORMAT = NumberFormat.getNumberInstance();
/**
* Computes a reasonable set of labels for a data interval and number of
* labels.
*
* @param start start value
* @param end final value
* @param approxNumLabels desired number of labels
* @return collection containing {start value, end value, increment}
*/
public static List<Double> getLabels(final double start, final double end,
final int approxNumLabels) {
FORMAT.setMaximumFractionDigits(5);
List<Double> labels = new ArrayList<Double>();
double[] labelParams = computeLabels(start, end, approxNumLabels);
// when the start > end the inc will be negative so it will still work
int numLabels = 1 + (int) ((labelParams[1] - labelParams[0]) / labelParams[2]);
// we want the range to be inclusive but we don't want to blow up when
// looping for the case where the min and max are the same. So we loop
// on
// numLabels not on the values.
for (int i = 0; i < numLabels; i++) {
double z = labelParams[0] + i * labelParams[2];
try {
// this way, we avoid a label value like 0.4000000000000000001 instead
// of 0.4
z = FORMAT.parse(FORMAT.format(z)).doubleValue();
} catch (ParseException e) {
// do nothing here
}
labels.add(z);
}
return labels;
}
/**
* Computes a reasonable number of labels for a data range.
*
* @param start start value
* @param end final value
* @param approxNumLabels desired number of labels
* @return double[] array containing {start value, end value, increment}
*/
private static double[] computeLabels(final double start, final double end,
final int approxNumLabels) {
if (Math.abs(start - end) < 0.0000001f) {
return new double[] { start, start, 0 };
}
double s = start;
double e = end;
boolean switched = false;
if (s > e) {
switched = true;
double tmp = s;
s = e;
e = tmp;
}
double xStep = roundUp(Math.abs(s - e) / approxNumLabels);
// Compute x starting point so it is a multiple of xStep.
double xStart = xStep * Math.ceil(s / xStep);
double xEnd = xStep * Math.floor(e / xStep);
if (switched) {
return new double[] { xEnd, xStart, -1.0 * xStep };
}
return new double[] { xStart, xEnd, xStep };
}
/**
* Given a number, round up to the nearest power of ten times 1, 2, or 5. The
* argument must be strictly positive.
*/
private static double roundUp(final double val) {
int exponent = (int) Math.floor(Math.log10(val));
double rval = val * Math.pow(10, -exponent);
if (rval > 5.0) {
rval = 10.0;
} else if (rval > 2.0) {
rval = 5.0;
} else if (rval > 1.0) {
rval = 2.0;
}
rval *= Math.pow(10, exponent);
return rval;
}
}
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