# Counting number of elements less than value across 2d matrix

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John Cruce on 20 May 2024
Edited: Adam Danz on 20 May 2024
I have a two-dimensional matrix of numbers size A(720,1440). I'd like to calculate the percent of values in part of the matrix -- i.e., from 401:440 and 1081:1360 -- where values are less than or equal to 5, exclusing NaN values.
In order to accomplish this, I'd like to first count the number of elements for this part of A (401:440,1081:1360) where values are less than 5, but omiting any NaN values.
I'm trying to do this using the sum function like below but I'm striking out. Any suggestions?
sum(A(401:440,1081:1360)<=5)

Adam Danz on 20 May 2024
Edited: Adam Danz on 20 May 2024
> I'd like to calculate the percent of values in part of the matrix -- i.e., from 401:440 and 1081:1360 -- where values are less than or equal to 5, exclusing NaN values.
A = randi(10,720,1440);
mu = mean(A(401:440,1081:1360)<=5,'all','omitnan')
mu = 0.4957
> I'd like to first count the number of elements for this part of A (401:440,1081:1360) where values are less than 5, but omiting any NaN values.
As you can see above, this step isn't needed. But for completeness,
count = sum(A(401:440,1081:1360)<=5,'all','omitnan')
count = 5552
To verity the mean computed above,
totalNumberOfElements = numel(A(401:440,1081:1360))
totalNumberOfElements = 11200
myConfirmed = count/totalNumberOfElements
myConfirmed = 0.4957

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