[R] difference

[William Dunlap]

You could use match() to find, for each row, the index of the first
row with the give row's year:

> d <- data.frame(year=c(rep(2001, 3), rep(2002, 3)),
                  num=c(25,75,150,30,85,95))
> indexOfFirstOfYear <- with(d, match(year, year))
> indexOfFirstOfYear
[1] 1 1 1 4 4 4
> d$diff <- d$num - d$num[indexOfFirstOfYear]
> d
  year num diff
1 2001  25    0
2 2001  75   50
3 2001 150  125
4 2002  30    0
5 2002  85   55
6 2002  95   65


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Thu, Oct 27, 2016 at 9:20 PM, Ashta <sewashm at gmail.com> wrote:

> Hi all,
>
> I want to calculate the difference  between successive row values to
> the first row value within year.
> How do I get that?
>
>  Here is    the sample of data
> Year   Num
> 2001    25
> 2001    75
> 2001   150
> 2002    30
> 2002    85
> 2002    95
>
> Desired output
> Year   Num  diff
> 2001    25       0
> 2001    75      50
> 2001  150    125
> 2002    30        0
> 2002    85      55
> 2002    95      65
>
> Thank you.
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>

	[[alternative HTML version deleted]]