[R] problem with diff

[Patrick Burns]

What I presume is the desired answer can be
arrived at via:

diff(as.numeric(row.names(info)))

The command:

m[,0]

returns a matrix with zero columns, but it still has
row names.  Performing 'diff' on this returns another
matrix with zero columns and one less row name.


Patrick Burns
patrick at burns-stat.com
+44 (0)20 8525 0696
http://www.burns-stat.com
(home of S Poetry and "A Guide for the Unwilling S User")

Fred J. wrote:

>dear R users
> 
> I am having a problem with the output of diff for a numeric vector
> which has the values (2,4,6,7), one expects to get 2 2 1 but I am
> getting 4 6 7, here is the setup.
> 
> 
> info <- with(rle(x),
>      data.frame(value = values,
>                 start = cumsum(lengths)-lengths+1,
>                 end = cumsum(lengths)
>                 )[lengths > 1,]
>      );
> > x <- c(3,4,4,4,4,5,7,7,0,1,1,2,2,2);
> > info
>   value start end
> 2     4     2   5
> 4     7     7   8
> 6     1    10  11
> 7     2    12  14
> 
> #since I cann't get the first column of info, I cast
> info into a matrix
> > m <- as.matrix(info); 
> > diff(m[,0])
> 
> 4
> 6
> 7
> 
> any idea why this is happening? and how to get the 
> correct diff.
> 
> 
> thank you
>			
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