[R] resizing data

[David Winsemius]

On Jan 25, 2013, at 2:29 PM, emorway wrote:

> I played around with your example on the smaller dataset, and it seemed like
> it was doing what I wanted.  However, applying it to the larger problem, I
> didn't  get a resized 2D dataset that preserved the order I was hoping for.
> Hopefully the following illustrates the larger problem:
> 
> x<-matrix(0,nrow=29328,ncol=7)
> 
> # Now set the 70,000th element to 1 to find out where it ends up?
> # Iterating on columns first, then rows, the 70,000th element is
> # at index [10000,7]

In an R matrix the "70,000"th element of a matrix with those dimensions would be in the 3rd column.

> 
> x[10000,7]<-1

That's not the 70000th element. its the (29328*6+1)th element. Given your  demonstrated misconceptions about R matrices and their column-major ordering I do not think I need to proceed further. Do some more self-study on R matrices.

> y<-t(matrix(x,nrow=546))
> dim(y)
> # [1] 376 546
> 
> # Does 1 appear at index [129,112] as I expect
> # (128 complete rows x 546 cols = 69888 + 112 = 70,000) thus, row 129, col
> 112
> y[129,112]
> # [1] 0
> 
> # No, so where is it? 
> grep(1,y)
> # [1] 123293
> 
> Where is that?
> 
> 
> 
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David Winsemius
Alameda, CA, USA