R help - May 2009 - Relative subscripts?

Dear R-helpers,

I have a dataframe with several columns, one of which is called LENGTH.

I would like to make a new column called DIFF containing the value of
LENGTH minus LENGTH in the previous row, like this:

  ID LENGTH DIFF
1  1     10   NA
2  2     15    5
3  3     20    5
4  4     12   -8
5  5     18    6

I'd like to think there are "relative subscripts" in R but I
can't
find any reference to such a thing.

Any help solving this problem would be much appreciated, thanks!

Mark Na

?diff
> x
  ID LENGTH DIFF
1  1     10   NA
2  2     15    5
3  3     20    5
4  4     12   -8
5  5     18    6
> x <- x[,-3]
> x
  ID LENGTH
1  1     10
2  2     15
3  3     20
4  4     12
5  5     18
> x$DIFF <- c(NA, diff(x$LENGTH) )
> x
  ID LENGTH DIFF
1  1     10   NA
2  2     15    5
3  3     20    5
4  4     12   -8
5  5     18    6


On Tue, May 5, 2009 at 7:00 PM, Mark Na <mtb954@gmail.com> wrote:
> Dear R-helpers,
>
> I have a dataframe with several columns, one of which is called LENGTH.
>
> I would like to make a new column called DIFF containing the value of
> LENGTH minus LENGTH in the previous row, like this:
>
>  ID LENGTH DIFF
> 1  1     10   NA
> 2  2     15    5
> 3  3     20    5
> 4  4     12   -8
> 5  5     18    6
>
> I'd like to think there are "relative subscripts" in R but I
can't
> find any reference to such a thing.
>
> Any help solving this problem would be much appreciated, thanks!
>
> Mark Na
>
> ______________________________________________
> R-help@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<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

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