Extracting every n number of column from matrix matlab

0 down vote favorite I need to extract every n number of column from my matrix. Please note that not every nth column. For example I have a matrix:

A =
     1    23    34    53    67    45    67    45
    12    34    45    56    67    87    98    12
     1     2     3    45    56    76    87    56
And I want to extract each 3 column, so my data should be like:

X =
     1    23    34    67    45    67
    12    34    45    67    87    98
     1     2     3    56    76    87
So I would skip 4th column then 8th column and so on. I know how to extract every nth column and row but I couldn't figure it out what I need. Appreciated for your help

Answer 1

[Ameer Hamza]

Here is a general solution to your problem in which you can specify how many columns to keep and how many to delete

colToKeep = 2;
colToDelete = 3;

ColIndex = mod( 0:size(A,2)-1, colToKeep+colToDelete ) < colToKeep;

A(:, ~ColIndex) = [];

Use colToKeep and colToDelete to specify the values.

[Aybars]

Hi Ameer,

 Thanks for your answer. Where do I need to use the ColIndex ? 
replace with ~m ?

[Ameer Hamza]

I made a mistake while pasting. I have edited the answer.

[Aybars]

I think you also don't need the "~". Just ColIndex seems working well. Thank you very much

[Ameer Hamza]

You are welcome. If you remove "~" the deleted columns will also change.

[Ee Woon Lim]

How do we do this for rows?

[Ameer Hamza]

Just take the transpose of the matrix and apply the same method. At the end take the transpose again to get the correct matrix.

Answer 2

[Yuvaraj Venkataswamy]

Answer is below where A is a your matrix.

if true
  n=4;
  A =[1    23    34    53    67    45    67    45

    12    34    45    56    67    87    98    12

     1     2     3    45    56    76    87    56]
    A(:,n:n:end) =[]
end

[Aybars]

Hi, Thank you very much for your answer. It is correct. But in that case, how can I adjust the number of column that I want to skip ? For example I would like to take first 2 columns, then skip 3 columns then take 2 columns again.

Answer 3

[Guillaume]

X = A;
X(:, 4:4:end) = [];

[Aybars]

Hi, Thank you very much for your answer. It is correct. But in that case, how can I adjust the number of column that I want to skip ? For example I would like to take first 2 columns, then skip 3 columns then take 2 columns again.