Select range of rows and store them

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Enzo
Enzo 2022-10-27
评论： Enzo 2022-10-28
Hello everyone,
that's the issue:
I have a matrix, let's call it Ch = 1000 x 33. In column 33, I have spotted some values using a threshold (MinPeakHeight function), which returns the location (lc) of these rows (let's call them rows_X). Now, using these indices, I would like to retain all the values within 3 rows before rows_X and 4 rows after every rows_X (the value inside rows_X must be retained as well). Any help will be very appreciated!!
Ex: let's take the following matrix. I have spotted all the values in column 6 greater than 7.Now I know these values lies in rows 3 and 8. I want to retain/store in different variables all the values in rows 3 and 8, plus all the values in the 2 rows before rows 3 and 8, and in 2 rows after rows 3 and 8.
Ch:
1 4 5 4 8 4
2 5 5 4 9 4
3 5 5 5 5 8
4 6 5 6 5 4
5 6 5 6 5 4
6 6 5 6 5 5
7 7 5 6 5 5
8 6 7 6 5 8
9 3 3 3 3 3
10 3 3 4 4 3
the final output should look like this:
rows_a =
1 4 5 4 8 4
2 5 5 4 9 4
3 5 5 5 5 8
4 6 5 6 5 4
5 6 5 6 5 4
rows_b =
6 6 5 6 5 5
7 7 5 6 5 5
8 6 7 6 5 8
9 3 3 3 3 3
10 3 3 4 4 3
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enzo
enzo 2022-10-27
@Matt J the first one was the actual scenario. The sample, where I asked minus 2 ans plus 2 rows from row_x is just for demonstrational purpose and in order to be easier to be shown to the matlab community
Enzo
Enzo 2022-10-27
@Matt J do you have any tips? please, fell free to share any doubt about this task

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采纳的回答

David Hill
David Hill 2022-10-27
编辑：David Hill 2022-10-27
Ran in:
Use of cell array for storage incase the sizes are not equal. If the sizes will always be the same, you could store in 3D-matrix.
Ch=[1 4 5 4 8 4
2 5 5 4 9 4
3 5 5 5 5 8
4 6 5 6 5 4
5 6 5 6 5 4
6 6 5 6 5 5
7 7 5 6 5 5
8 6 7 6 5 8
9 3 3 3 3 3
10 3 3 4 4 3];
idx=find(Ch(:,6)>7);
for k=1:length(idx)
S{k}=Ch(max(1,idx(k)-2):min(size(Ch,1),idx(k)+2),:);%max and min to protect against to low or high of indexing
end
S{1}
ans = 5×6
1 4 5 4 8 4 2 5 5 4 9 4 3 5 5 5 5 8 4 6 5 6 5 4 5 6 5 6 5 4
S{2}
ans = 5×6
6 6 5 6 5 5 7 7 5 6 5 5 8 6 7 6 5 8 9 3 3 3 3 3 10 3 3 4 4 3
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David Hill
David Hill 2022-10-27
It matches the output above other than assigning different variables (should index into a single variable and not have dynamic variable names). What are you trying to do once you have the various matrices?
Enzo
Enzo 2022-10-28
hi @David Hill thanks for your time. I have tried again and, as I am using huge data files, matlab send me this error code
Out of memory.
reasonably, I have to keep it simple without killing the ram

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