Try this: subset(as.data.frame(xtabs( ~ city + var, df)), !Freq)
On Wed, Feb 2, 2011 at 1:49 PM, H Roark <hrbuil...@hotmail.com> wrote: > > I have a data set covering a large number of cities with values for > characteristics such as land area, population, and employment. The problem I > have is that some cities lack observations for some of the characteristics > and I'd like a quick way to determine which cities have missing data. For > example: > > city<-c("A","A","A","B","B","C") > var<-c("sqmi","pop","emp","pop","emp","pop") > value<-c(10,100,40,30,10,20) > df<-data.frame(city,var,value) > > In this data frame, city A has complete data for the three variables, while > city B is missing land area, and city C only has population data. In the > full data frame, my approach to finding the missing observations has been to > create a data frame with all combinations of 'city' and 'var', merge this > onto the original data frame, and then extract the observations with missing > data for 'value': > > city_unq<-c("A","B","C") > var_unq<-c("sqmi","pop","emp") > comb<-expand.grid(city=city_unq,var=var_unq) > > mrg<-merge(comb,df,by=c("city","var"),all=T) > missing<-mrg[is.na(mrg$value),] > > This works, but on a large dataset it gets slow and I'm looking for a a > more efficient way to achieve this same result. Any suggestions would be > much appreciated. > > Cheers > > [[alternative HTML version deleted]] > > ______________________________________________ > 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. > -- Henrique Dallazuanna Curitiba-Paraná-Brasil 25° 25' 40" S 49° 16' 22" O [[alternative HTML version deleted]]
______________________________________________ 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.