how to remove specific rows of columns
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Hey everyone. I have one matrix [a] with 5 columns. i am removing some rows of b=a(:,4) based on some threshold, and then I need to construct a new matrix with the new column 4 . but I also need to include the first three columns. how can I remove the same rows from the first three columns? Thanks !
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James Tursa
2017년 2월 27일
편집: James Tursa
2017년 2월 27일
Save the indexing that you use to do the removing, and then apply that to the original matrix during the reconstruction. E.g.,
>> a = reshape(1:30,6,5)
a =
1 7 13 19 25
2 8 14 20 26
3 9 15 21 27
4 10 16 22 28
5 11 17 23 29
6 12 18 24 30
>> b = a(:,4)
b =
19
20
21
22
23
24
>> rows_to_remove = mod(b,2)==1
rows_to_remove =
1
0
1
0
1
0
>> result = [a(~rows_to_remove,1:3) b(~rows_to_remove)]
result =
2 8 14 20
4 10 16 22
6 12 18 24
Or suppose instead of logical indexing as in the above example, you had row numbers to remove. E.g.,
rows_to_remove = [1 3 5]
Then just transform this into a logical indexing vector first. E.g.,
rows_to_remove = ismember(1:size(a,1),rows_to_remove)
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