Variance calculation

Question

I have one variable named Xvehicle which is pick point of the histogram. So my question is with 'Xvehicle' how to calculate variance of the histogram?

Vulpes · Answer

Suppose XVehicle is an array of the pick points of the histogram and the corresponding frequencies of each pick point are given in another array YVehicle. Then the variance of the histogram can be calculated using the following C# code: double sumXY = 0.0; double sumY = 0.0; for(int i = 0; i { sumXY += XVehicle[i] * YVehicle[i]; sumY += YVehicle[i]; } double mean = sumXY/sumY; double variance = 0; for(int i = 0; i { double deviation = XVehicle[i] - mean; variance += deviation * deviation * YVehicle[i]; } variance /= sumY; For example if we use the data in this link: http://phys.columbia.edu/~tutorial/estimation/tut_e_2_4.html double[] XVehicle = {3.4 3.5 3.6 3.7 3.8 3.9}; double[] YVehicle = {1 2 3 2 1 1}; we get: variance = 0.0201 and the standard deviation is then the square root of this which is: 0.141774468787578 (approximated to 0.14 in the link).