help with subset Dates in R

[Brett Scheffers]

Hello Everyone

Happy Holidays!

I'm trying to select data between two dates 2011-29-06 to 2011-25-08  (y/d/m) and am having trouble. I'm a novice R user and dates in R just confuse me. Any help would be much appreciated.
 
The object I'm working from is derived from multiple .csv files in a single folder and then arranging them in the following:

alldata<-c()
for (ii in 1: length(f)){
  d<-read.csv(file=f[ii], header=T)
  t1<-sub(pattern=":", replacement=".", x=d$DateTime)
  t1<-as.vector(regexpr(pattern=":", text=t1))
  fmat<-ifelse(t1==-1, "%d/%m/%Y %H:%M", "%d/%m/%Y %H:%M:%S")
  d$tdate=strptime(d$DateTime, format=fmat)
  d$date<-as.Date(format(d$tdate, "%d/%m/%y"), format="%d/%m/%y")
  d$mdata<-rep(test2[ii], nrow(d))
  d$elev<-as.numeric(rep(test3[ii], nrow(d)))
  d$gc<-rep(test4[ii], nrow(d))
  if(nrow(d)==0) print(ii)
  alldata<-rbind(alldata, d) 
}

The alldata object are in the following data format:

str(alldata)
'data.frame':	578229 obs. of  8 variables:
 $ DateTime: Factor w/ 11390 levels "1/8/2011 0:14",..: 3038 3039 3040 3041 3042 3043 3044 3045 3046 3047 ...
 $ Temp..C.: num  20.1 20.1 20.6 20.6 20.6 ...
 $ Hum.... : num  97.1 96.7 97.1 96.7 97.1 ...
 $ tdate   : POSIXlt, format: "2011-07-05 11:59:00" "2011-07-05 12:14:00" "2011-07-05 12:29:00" ...
 $ date    : Date, format: "2011-07-05" "2011-07-05" "2011-07-05" ...
 $ mdata   : chr  "1100TR1-Canopy" "1100TR1-Canopy" "1100TR1-Canopy" "1100TR1-Canopy" ...
 $ elev    : num  1100 1100 1100 1100 1100 1100 1100 1100 1100 1100 ...
 $ gc      : chr  "Canopy" "Canopy" "Canopy" "Canopy" ...

The data I'm interested in are the alldata$date data which as you can see are already in a date format by use of the as.Date().

I would like to subset the data from alldata$gc (which is either Canopy or Ground), alldata$elev (which all data are an elevation between 900 and 2100), and then the alldata$date (in my case dates from 2011-29-06 to 2011-25-08). 

My script is:
subdata <- subset(alldata, subset=(alldata$gc == 'Canopy') & alldata$elev == 1300 & alldata$date >= "2011-29-06" & alldata$date <= "2011-25-08" , select=c(Temp..C., elev, gc, date) )

this does not work.
The following error shows:
"Error in charToDate(x) : character string is not in a standard unambiguous format"

Again, any help that you can offer would be greatly appreciated.

Cheers
Brett Scheffers

[Phillips, Ben]

Brett. 

In you final subset you need to change your boundary dates into date objects. 

alldata$date >= as.Date("2011-29-06", format = "%Y-%d-%m")

B

Excuse the brevity: sent from my phone.

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[Stewart Macdonald]

Out of interest, does it work if you use "2011-06-29" instead of "2011-29-06"? It looks like R is trying to convert it to a date object automatically, but is getting confused. But as Ben said, it's better to explicitly convert it rather than rely on automatic and potentially ambiguous conversion.

Stewart