# Average of the nine surrounding cells

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Ahmed Abdulla on 29 May 2020
Commented: Stephen23 on 29 May 2020
I have two matrices, matrix1 contains genuine data and matrix2 is filled with 0's and a few 1's, i wanted to know if there is a way to calculate the average of all 9 cells surrounding the cell with the 1 in the matrix with the genuine data. i.e when a 1 is spotted in matrix2 then the average of the 9 surrounding cells to the corresponsinding cell in matrix1 is calculated.
Im not sure if this is clear

Stephen23 on 29 May 2020
Edited: Stephen23 on 29 May 2020
Use conv2 to calculate the averages, e.g.:
out = matrix2.*conv2(matrix1,ones(3,3),'same')/9;
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Stephen23 on 29 May 2020
Instead of dividing by 9 you could divide by a matrix of the same size, where each element's value gives the number that you want to divide by. Also note that the corners have 4, the sides 6, and the middle 9:
D = ones(size(matrix1))*6;
D(2:end-1,2:end-1) = 9;
D([1,end],[1,end]) = 4;
out = matrix2.*conv2(matrix1,ones(3,3),'same')./D;
Or if you have the image toolbox you could just use blockproc:

R2019b

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