On Thu, Feb 3, 2011 at 1:11 PM, David Winsemius <dwinsem...@comcast.net> wrote: > > On Feb 3, 2011, at 1:05 PM, Graves, Gregory wrote: > >> Yes, as far as I can tell, "sampling.date" is a character vector of the >> format "1/15/2008". It resides in the leftmost column of the tapply output. >> >> "station.code" are the A, B, C column headers which refer actual water >> quality station locations, and the values below those headers correspond to >> the "sampling.date" when samples were taken. Actually what I have done is >> to take the mid-point of each month and calculated its mean to deal with >> multiple samples taken in one month, and to generate NAs where no sample was >> taken by purposefully not adding the na.rm=T to the tapply command. >> >> Normally I would do this: >>> >>> rdate<-as.POSIXct(strptime(date,format="%m/%d/%Y")) #convert >>> sampling.date to date R can handle >>> plot(A~rdate) >> >> If I just submit station.code like >>> >>> A >> >> I get all the values for "Station A". >> >> It is in converting the sampling.date to an "rdate" that has me stumped. >> One reason being that in the tapply output the character vector >> representing date has no column name. I can't access that column. > > It looks like a zoo object. "zoo" objects hold their time values in the > rownames attribute. But since its not really ordered properly, it may just > be a table with rownames. The str() function applied to the object from > tapply would tell you the answer. >
Internally zoo objects hold their time index in the "index" attribute. > library(zoo) > dput(zoo(4:5)) structure(4:5, index = 1:2, class = "zoo") -- Statistics & Software Consulting GKX Group, GKX Associates Inc. tel: 1-877-GKX-GROUP email: ggrothendieck at gmail.com ______________________________________________ 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 and provide commented, minimal, self-contained, reproducible code.