[R] for 1:length and removing rows

[(Ted Harding)]

On 04-Sep-08 15:33:06, Markus Mühlbacher wrote:
> Hello everyone,
> I have a problem using a for-loop to go through a matrix. I want to
> remove all rows with a sum of 0.
> What I do is basically:
> 
> for(i in 1:length(data))
> {
>    if(sum(add(data[i,]) == 0)
>    {
>       data <- data[-i,]
>    }
> }
> 
> I get a error message: "Error in `[.data.frame`(data, i) : undefined
> columns selected", because the length is reduced when removing in the
> if-clause.
> 
> How do I make this?

The function rowSums() gives you the row-sums of a matrix, which
you can test for "==0", and carry on from there. Example:

  M<-matrix(c(1,2,3,0,-1,-2,-3,1,-2,3,0,1,2,-1),ncol=2)

  M
#      [,1] [,2]
# [1,]    1    1
# [2,]    2   -2
# [3,]    3    3
# [4,]    0    0
# [5,]   -1    1
# [6,]   -2    2
# [7,]   -3   -1

  ix<-which(rowSums(M)==0)

  M[-ix,]
#      [,1] [,2]
# [1,]    1    1
# [2,]    3    3
# [3,]   -3   -1

Hoping this helps!
Ted.

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Date: 04-Sep-08                                       Time: 16:49:46
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