Possible Duplicate:
Simple statistics - Java packages for calculating mean, standard deviation, etc
I have a vector of some doubles (1.1,2,3,5). How can I calculate the variance, median, and standard deviation?
Java or C++ or even pseudo code would do.
public class Statistics {
double[] data;
int size;
public Statistics(double[] data) {
this.data = data;
size = data.length;
}
double getMean() {
double sum = 0.0;
for(double a : data)
sum += a;
return sum/size;
}
double getVariance() {
double mean = getMean();
double temp = 0;
for(double a :data)
temp += (a-mean)*(a-mean);
return temp/(size-1);
}
double getStdDev() {
return Math.sqrt(getVariance());
}
public double median() {
Arrays.sort(data);
if (data.length % 2 == 0)
return (data[(data.length / 2) - 1] + data[data.length / 2]) / 2.0;
return data[data.length / 2];
}
}
To calculate the mean, loop through the list/array of numbers, keeping track of the partial sums and the length. Then return the sum/length.
double sum = 0.0;
int length = 0;
for( double number : numbers ) {
sum += number;
length++;
}
return sum/length;
Variance is calculated similarly. Standard deviation is simply the square root of the variance:
double stddev = Math.sqrt( variance );
Source: Stackoverflow.com