Re: column elimination

[Ben Abbott]

On Jul 19, 2010, at 6:48 PM, Victor Carreto Pavon wrote:

> On 19/07/2010, at 07:25 p.m., James Sherman Jr. wrote:
> 
>> On Mon, Jul 19, 2010 at 6:09 PM, Victor Carreto Pavon <address@hidden> wrote:
>> thanks for the comment I certanly did not knew that A(:,[1 4 6]) will return 
>> columns 1, 4 and 6... but let's say that what I am looking for are the 
>> remaining columns from the original matrix A there fore what I want are 
>> columns 2, 3, 5...
>> 
>> I don't think I'm getting exactly what you're looking for.  Do you want all 
>> the columns except 1 and 4?  This can be done a couple ways, the most 
>> straight forward probably being:
>> cols = size(A, 2);
>> A(:, [2, 3, 5:cols])
>> 
>> Is this what you are asking?
> 
> yes... that is right; I want all the columns except 1 and 4 in this case, but 
> maybe in the next case I might not want all the columns except 3 and 5. then 
> the notation A(:,[2,3,5:cols]) will no longer be useful. 
> 
> Do you know can I make it generic so it will work for any combination?
> 
> and thanks for answering. 

If you just want to eliminate columns then ...

A(:,[1,4]) = [];

... will eliminate columns 1 and 4.

octave:12> A = rand (6)
A =

   0.704284   0.635028   0.998254   0.200610   0.963574   0.578821
   0.943338   0.427950   0.145803   0.477948   0.025938   0.331903
   0.894940   0.140775   0.518609   0.038302   0.232539   0.379098
   0.353322   0.360688   0.432351   0.328230   0.998258   0.844157
   0.682254   0.851592   0.945387   0.380018   0.812283   0.725536
   0.473056   0.776754   0.800953   0.717851   0.163009   0.649179

octave:13> A(:,[1,4]) = []
A =

   0.635028   0.998254   0.963574   0.578821
   0.427950   0.145803   0.025938   0.331903
   0.140775   0.518609   0.232539   0.379098
   0.360688   0.432351   0.998258   0.844157
   0.851592   0.945387   0.812283   0.725536
   0.776754   0.800953   0.163009   0.649179

Ben