R help - Jun 2011 - Removing rows of zeros from a matrix

Hi,
Can someone tell me how to remove rows of zeros from a matrix?
For example if I have the following matrix,

0 0
0 1
2 8
0 0
4 56

I should end up with
0 1
2 8
4 56

-- 
Thanks,
Jim.

	[[alternative HTML version deleted]]

Assuming the matrix is named X:

X[which(rowSums(X) > 0),]

should work.

Also, this list is a text-only list. As you are using gmail, sending
text only messages is very easy, and may clear confusion in future
posts.

HTH,

Jon

On Thu, Jun 2, 2011 at 11:23 AM, Jim Silverton <jim.silverton at
gmail.com> wrote:
> Hi,
> Can someone tell me how to remove rows of zeros from a matrix?
> For example if I have the following matrix,
>
> 0 0
> 0 1
> 2 8
> 0 0
> 4 56
>
> I should end up with
> 0 1
> 2 8
> 4 56
>
> --
> Thanks,
> Jim.
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
==============================================Jon Daily
Technician
==============================================#!/usr/bin/env outside
# It's great, trust me.

On Thu, Jun 02, 2011 at 11:23:28AM -0400, Jim Silverton
wrote:
> Hi,
> Can someone tell me how to remove rows of zeros from a matrix?
> For example if I have the following matrix,
> 
> 0 0
> 0 1
> 2 8
> 0 0
> 4 56
> 
> I should end up with
> 0 1
> 2 8
> 4 56
Hi.

Try the following

  a <- matrix(c(0, 0, 2, 0, 4, 0, 1, 8, 0, 56), ncol=2)
  a[rowSums(a != 0) != 0, ]

Hope this helps.

Petr Savicky.

On Jun 2, 2011, at 11:35 AM, Petr Savicky wrote:
> On Thu, Jun 02, 2011 at 11:23:28AM -0400, Jim Silverton wrote:
>> Hi,
>> Can someone tell me how to remove rows of zeros from a matrix?
>> For example if I have the following matrix,
>>
>> 0 0
>> 0 1
>> 2 8
>> 0 0
>> 4 56
>>
>> I should end up with
>> 0 1
>> 2 8
>> 4 56
>
> Hi.
>
> Try the following
>
>  a <- matrix(c(0, 0, 2, 0, 4, 0, 1, 8, 0, 56), ncol=2)
>  a[rowSums(a != 0) != 0, ]
To avoid removing rows where non-zero elements do sum to 0 one could  
use the only slightly longer test that first converts "a" to logical:

  a <- matrix(c(1, 0, 2, 0, 4, -1, 1, 8, 0, 56), ncol=2)

  a[ rowSums(a==0) != ncol(a), ]
      [,1] [,2]
[1,]    1   -1
[2,]    0    1
[3,]    2    8
[4,]    4   56

-- 
David Winsemius, MD
West Hartford, CT