Using logical index matrix to create another matrix with values

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Hi All,
I have a matrix (E) with 180 x45 with values. I would like to create another matrix where the values are >1E9. First I found the indexes (idx) of the values that are >1E9 in matrix E. Now I would like to use that matrix index (idx) to create the another matrix (E2) that have the values that are >1E9. But it created just one column data insted not a matrix. How can I solve this?
Thank you
idx=E>1E9;
E2=E(idx);
Birsen

Accepted Answer

Steven Lord
Steven Lord on 3 Aug 2022
What do you want the elements that did not satisfy the condition in your original matrix to be in the new matrix? You can't have a "Swiss cheese" matrix (one with holes in it.)
Here's one example that fills in where those holes would have been with NaN values.
A = magic(4)
A = 4×4
16 2 3 13 5 11 10 8 9 7 6 12 4 14 15 1
ind = A > 8
ind = 4×4 logical array
1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0
B = NaN(4)
B = 4×4
NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN
B(ind) = A(ind)
B = 4×4
16 NaN NaN 13 NaN 11 10 NaN 9 NaN NaN 12 NaN 14 15 NaN
Note that if you'd tried to use ind to extract just those elements of A, you are correct that you'd receive a vector. Remember, no holes allowed.
C = A(ind)
C = 8×1
16 9 11 14 10 15 13 12

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