MATLAB: copy a specific portion of an array

Question

I am trying to copy a few elements from a matrix, but not a whole row, and not a single element.

For example, in the following matrix:

How would I copy out just the following data?

b = 1
    3
    5

i.e. rows 1:3 in column 1 only... I know that you can remove an entire column like this:

b = a(:,1)

... and I appreciate that could just do this and then dump the last two rows, but I'd like to use more streamlined code as I am running a very resource-intensive solution.

You already wrote an answer :) b=a(1:3,1); In order to remove a column you can 'unset' it by a(:,1)=[]; — Cheery
– Cheery, Commented Feb 10, 2012 at 2:24

eternaln00b · Accepted Answer · 2012-02-10 03:30:38Z

5

Elements in a matrix in MATLAB are stored in column-major order. Which means, you could even use a single index and say:

b = a(1:3);

Since the first 3 elements ARE 1,3,5. Similarly, a(6) is 2, a(7) is 4 etc. Look at the sub2ind method to understand more:

http://www.mathworks.com/help/techdoc/ref/sub2ind.html

answered Feb 10, 2012 at 3:30

eternaln00b

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ivancho · Accepted Answer · 2012-02-10 02:16:50Z

1

You are not "removing" the second column, you are referencing the other column.

You should read some of the Matlab docs, they provide some help about the syntax for accessing portions of matrices:

http://www.mathworks.com/help/techdoc/learn_matlab/f2-12841.html#f2-428

answered Feb 10, 2012 at 2:16

ivancho

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