help with for loop: new column giving count of observation for each SITEID

Not quite,
 I need it like this, a new number for each ordered year in the sequence within each site, regardless of what the years are,  and to retain the RchID column.

RchID   site    year    index
1       A       2002    1
2       A       2004    2
3       A       2005    3
4       B       2003    1
5       B       2006    2
6       B       2008    3
7       C       2002    1
8       C       2003    2
9       C       2004    3


Thanks so much for you help!

-----Original Message-----
From: William Dunlap [mailto:wdunlap at tibco.com]
Sent: Tuesday, October 30, 2012 1:07 PM
To: Meredith, Christy S -FS; r-help at R-project.org
Subject: RE: [R] help with for loop: new column giving count of observation for each SITEID

Is this what you want?

  > withinGroupIndex <- function(group, ...) ave(integer(length(group)), group, ..., FUN=seq_along)
  > site <- c("A","A","C","D","C","A","B")
  > data.frame(site, index=withinGroupIndex(site))

    site index
  1    A     1
  2    A     2
  3    C     1
  4    D     1
  5    C     2
  6    A     3
  7    B     1

You can add more arguments if the groups depend on more than one value:

  > year <- rep(c(1985, 2012), c(4,3))
  > data.frame(site, year, index=withinGroupIndex(site, year))

    site year index
  1    A 1985     1
  2    A 1985     2
  3    C 1985     1
  4    D 1985     1
  5    C 2012     1
  6    A 2012     1
  7    B 2012     1

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

-----Original Message-----
From: r-help-bounces at r-project.org
[mailto:r-help-bounces at r-project.org] On Behalf Of Meredith, Christy S
-FS
Sent: Tuesday, October 30, 2012 11:17 AM
To: r-help at R-project.org
Subject: [R] help with for loop: new column giving count of
observation for each SITEID


Hello,
I think this is easy, but I can't seem to find a good way to do this
in the R help. I have a list of sites, with multiple years of data for
each site id. I want to create a new column that gives a number
describing whether it is the 1st year ("1" ) the data was collected
for the site, the second year ("2"), etc. I have different years for
each siteid, but I don't care which year it was collected, just the order that it is in for that siteid.  This is what I have so far, but it doesn't do the analysis separately for each SiteID.

indexi<-indexg[order(indexg$SiteID,indexg$Yr),]

obs=0
indexi=na.omit(indexi)
for(i in 1:length(indexi$SiteID)){
obs=obs+1
indexi$obs[i]=obs
}


Thanks for any help you can give.

Christy Meredith
USDA Forest Service
Rocky Mountain Research Station
PIBO Monitoring
Data Analyst
Voice: 435-755-3573
Fax: 435-755-3563





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