# (Solved) How to plot the variance of elements in each bin of histogram?

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gunjanthesystem on 24 Mar 2014
Edited: gunjanthesystem on 25 Mar 2014
Data: Array of real valued numbers. (say XArray)
To plot: A histogram superimposed with the plot of variance(/IQR) of elements
in each bin.
Also, how could i plot frequency on x-axis instead of y-axis.
Sincerely
gunjanthesystem on 25 Mar 2014
(Solution) using histc to get 'binIndex', i,e. the bin index of each element in the data array. Bin index indicates in which bin that particular element was put.
[~,binIndex]= histc(XArray,binranges);
varMatrix=zeros(1,numberOfBins); % filled with dummy values
for iterator=1:max(binIndex)
varMatrix(iterator)=var(XArray(find(binIndex==iterator)));
end
%Now the varMatrix will contains the variance for each bin.

Chandrasekhar on 24 Mar 2014
plot the histogram using hist command then hold the figure using hold on. then plot the variant using plot command
hist(array)
hold
plot(frequency,variance)

Image Analyst on 24 Mar 2014
To get the counts:
counts = hist(data, numberOfBins);
To get the variance of the counts
countVariance = var(counts);
##### 2 CommentsShowHide 1 older comment
Image Analyst on 24 Mar 2014
You need to know the value that defines the start and stop value for each bin. Let's say it's v1 and v2. Then extract all the values in that range from your data
inRange = data > v1 & data < v2;
Now get the variance
dataRangeVariance = var(data(inRange));
This gets the variance of only those elements that fell into that particular bin.