Replace values on a column filtering with a value

Question

Alessandro Togni 2021-1-27

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回答： Daniel Catton 2021-1-27

Hi,

i have a matrix with 56 columns and want to replace with NaN values on a column N corresponding to positions on another column M containing values > of a threshold.

Let's say: if the i-th value of the column 56 is greater than threshold, replace the i-th value of the column N with NaN.

Logical indexing would be better.

Doing this i'm selecting the values greater than 8 on the columns, erasing the others.

R_mod=R(R(:, 56) > 8.0, :)

Thanks in advance,

Alessandro

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Answer 1

Mathieu NOE 2021-1-27

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hello

something like that :

%% some dummy data
A = (1:10);
In_Matrix =A'*A;
%% main code %%
Out_Matrix = In_Matrix;
threshold = 45;
col_index_to_test = 9;     % column index where you do the test  > threshold
col_index_to_replace = 8;  % column indexwhere you want to replace values by NaN
ind = find(In_Matrix(:,col_index_to_test) > threshold);
Out_Matrix(ind,col_index_to_replace) = NaN;

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Answer 2

Daniel Catton 2021-1-27

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I think I understand what you mean, this works for my understanding of your problem but let me know if I have misunderstood. The user will input their values of 'YourMatrix', 'M' and 'N' and the script will output your 'NewMatrix'.

YourMatrix = ;
M = ;
N = ;
[x,y] = size(YourMatrix);
NewMatrix = YourMatrix;
for i = 1:x
    j = YourMatrix(i,M);
    if j <= 8
        NewMatrix(i,N) = NaN;
    end
end