How to select specific columns in a matrix and create a new one

Hello, I am very new to Matlab, so my question could be too elementary... I have a huge matrix made of 7 rows. In the last row, there are only 1 or 0. I need to create a new matrix from the original one, taking only the columns which last row value is 1. Or, in other terms, I want to discard all those columns whose last value is 0. Is there a simple way to do it?

Thank you

[Paola]

This is an example of my matrix (actually I have hundreds of columns and not just 4 as here).

     1     2     3     4
     4     5     6     8
     7     8     9     8
     2     3     7     4
     5     7     2     9
     3     5     1     7
     1     0     0     1

I want to create a new matrix that contains only the columns whose last number is 1. The result would be this one:

     1     4
     4     8
     7     8
     2     4
     5     9
     3     7
     1     1

To obtain this example I just selected manually the 2 columns to show, but, since I have a huge matrix and I can't write and check every single column...

Answer 1

[Guillaume]

Either

newmatrix = yourmatrix(:, yourmatrix(end, :) == 1)

Or

newmatrix = yourmatrix(:, logical(yourmatrix(end, :)))

will do it.

This is very basic indexing so you should go through the Getting Started Tutorial. What the above does is:

• get a logical row vector of which columns are 1 and which are 0, using either yourmatrix(end, :) == 1 or logical(yourmatrix(end, :)),
• then use that logical vector of 0 and 1 to filter the column with yourmatrix(:, logicalvector)

[Paola]

Your answer is very clear. thanks a lot!