# How to find a unexpected high value and turn it to zero?

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Masoud Taleb on 26 Apr 2020
Commented: Les Beckham on 27 Apr 2020
Hello
I have a matrix with 4 columns. I want to code it in a way that column 4th to be checked by matlab and unwanted high value (in this example: 80) to be descovered and changes to zero. At the end, this matrix to be saved as csv file. (Since data are experimental, there is no rule to find this kind of error values in 4th column. I can say, it is at least 3 times bigger than avareage value of the column)
My current code works, but want to know if there is a better way to handel this? Maybe my loop is incorrect. I will be grateful if someone can help in this.
A = [2 3 4 2;5 6 7 3;8 9 0 6; 5 6 1 80;2 3 8 5;3 5 13 4]
as = length (A(:,4))
M = mean (A(:,4))
for i = 1:as
Max = max (A(:,4))
if Max > 3*M
A(A==Max)=0
else end
end
fname = sprintf('new.csv');
csvwrite (fname,A); % Write to CSV file

Les Beckham on 26 Apr 2020
Edited: Les Beckham on 26 Apr 2020
Here is a way to do this without a loop (using logical indexing)
A = [2 3 4 2;5 6 7 3;8 9 0 6; 5 6 1 80;2 3 8 5;3 5 13 4]
idx = A(:,4) > mean(A(:,4))*3; % determine indices of outliers
A(idx,4) = 0; % set outliers equal to zero
fname = sprintf('new.csv');
csvwrite (fname,A); % Write to CSV file
You can also use the isoutlier function:
A(isoutlier(A(:,4)), 4) = 0;
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Les Beckham on 27 Apr 2020
You are welcome. Glad I could help.