This example was really bugging me, as I had a hard time believing that
[math] and Excel could be so far out of whack. I did a simple experiment
and posted the results on my blog:
http://www.researchkitchen.co.uk/blog/archives/75
Jeff, this may show that the issue is likely somewhere else in your
code. If you're still having issues, you may actually want to post the
actual data used, if possible, so somebody else can verify it with your
data.
Cheers
Rory
Jeff Drew wrote:
I'm having a weird problem when using the commons math package. When
I run
statistics using the Commons math, then compare the results to Excel,
I get
different standard deviation and median, but min, max, and count are the
same. I'd appreciate any ideas on how Commons Math and Excel differ in
these calculations.
MEDIAN: Excel: 468,231 CommonsMath: 485,711
STD: Excel: 11,861 CommonsMath: 10,678
The data set is 18,000 integers so I won't include those. They are
mostly 6
digit numbers. Here's the code:
import org.apache.commons.math.stat.descriptive.moment.StandardDeviation;
import org.apache.commons.math.stat.descriptive.rank.Max;
import org.apache.commons.math.stat.descriptive.rank.Median;
import org.apache.commons.math.stat.descriptive.rank.Min;
import gnu.trove.TDoubleHashSet;
public class ExampleForMailingList {
StandardDeviation std = new StandardDeviation( );
Min min = new Min( );
Max max = new Max( );
Median medianInstance = new Median();
private double minimum = 0;
private double maximum = 0;
private double standardDev = 0;
private double median = 0;
private boolean isCalcDone = false;
private double count = 0;
/**
* <code>data</code> If the length is zero, then only 0 measurements
were added.
*/
TDoubleHashSet data = new TDoubleHashSet( );
/**
* If the <code>measurement</code> is greater than 0, then add it
to the
data.
*
* @param measurement
*/
public void addMeasurement( int measurement ) {
data.add( measurement );
count++;
}
/**
* Must be called before using the getters. This method calculates
the
statistics.
*/
public void calculate() {
try {
double[] dataArray = data.toArray( );
minimum = min.evaluate( dataArray );
maximum = max.evaluate( dataArray );
standardDev = std.evaluate( dataArray );
median = medianInstance.evaluate(dataArray);
isCalcDone = true;
} catch ( RuntimeException e ) {
// TODO Auto-generated catch block
e.printStackTrace( );
}
} // calculate
public double getMinimum() throws CalcNotDoneException {
return minimum;
} // get minimum
public double getMaximum() throws CalcNotDoneException {
return maximum;
} // get maximum
public double getStd() throws CalcNotDoneException {
return standardDev;
} // get std
public double getMedian() throws CalcNotDoneException {
return median;
} // get median
/**
* Converts a result set into a set of statistics which a table model
consumes. Calculates: <br>
* 1. min <br>
* 2. average <br>
* 3. max <br>
* 4. median<br>
* 5. percent threshold violations <br>
* @param resultSetArg
* Results of an order table query
*/
public void processResults( ResultSet results,String column ) {
int value = Integer.MAX_VALUE;
try {
while ( results.next( ) ) {
value = ( int ) results.getLong( column );
if ( value > -1 ) {
addMeasurement( value );
}
}
} catch ( SQLException e ) {
// TODO Auto-generated catch block
e.printStackTrace();
} // while
} // processResults
public static void main( String[] args ) {
ExampleForMailingList example = new ExampleForMailingList();
example.processResults(ResultSet set,"columnA");
example.calculate( );
System.out.println("std: "+ example.getStd( ));
System.out.println("std: "+ example.getMedian( ));
}
}
Thanks!
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