How can I select particular elements by an increasing step in rows?
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ugur uresin
il 18 Apr 2018
Commentato: ugur uresin
il 18 Apr 2018
10 20 30
11 21 31
12 22 32
13 23 33
14 24 34
15 25 35
16 26 36
17 27 37
18 28 38
19 29 39
For example: I'd like to extract 4 elements in each column from the matrix above. Extracted elements would be (1,1),(2,1),(3,1),(4,1) for the 1st column, and (1,2),(3,2),(5,1),(7,1) for the 2nd column, and (1,3),(4,3),(7,3),(10,3). Example out is given below:
10 20 30
11 22 33
12 24 36
13 26 39
Note: I have hundreds of rows and columns. So, I need a generic solution.
Thank you.
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Stephen23
il 18 Apr 2018
Modificato: Stephen23
il 18 Apr 2018
This is easy using linear indexing (a loop is not required):
>> [M(1:10:end);M(2:11:end);M(3:12:end);M(4:13:end)] ans = 10 20 30 11 22 33 12 24 36 13 26 39
Note that M has 10 rows, so you can easily adjust the code I gave to work for any number of rows:
>> S = size(M,1); >> [M(1:S+0:end);M(2:S+1:end);M(3:S+2:end);M(4:S+3:end)] ans = 10 20 30 11 22 33 12 24 36 13 26 39
Note that this method only works if the number of columns is <= the number of rows.
To adjust for N elements from each column you can add a loop, either following the method above:
N = 4; Y = nan(N,size(M,2)); S = size(M,1); for k = 1:N Y(k,:) = M(k:S+k-1:end); end
or doing a naive implementation of what you explained in your question.
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