"I... cannot look it up in a book." Baloney! Read the R Language Definition manual section on indexing in the "Evaluation of Expressions" Chapter. Then ?lapply and ?"[[" -- and the relevant sections in "The Introduction to R" manual.
However, I will admit that it's tricky. The point to grasp -- described at various levels of detail in the above manuals and in numerous other resources that you can check out on the CRAN website -- is that y[["a"]] is just syntactic sugar for "[["(y,"a") . R is a "functional" language (mostly). So your lapply statement is just lapplying the "[[" function(extraction operator ) to the list of data frames. Cheers, Bert On Tue, Aug 7, 2012 at 12:06 PM, Kevin Chang <kchan...@uoguelph.ca> wrote: > Hello R users > > > > I recently learned how to use this command: > > > lapply(datum,"[[","ColumnName") > > > > Unfortunately, I don't know how exactly it works, what it's called (in > particular the "[[" part], and what other things you can do with it > (retrieve multiple columns?). > > > Given datum is a list of dataframes with the same column, but different > number of rows, > > > > lapply(datum,"[[","ColumnName"), > > > > Returns you a list of a particular column form each of your dataframes from > datum. > > > > I think this is a really useful command, and would like to learn more about > it. > Unfortunately I don't know what subject or topic it is under and cannot look > it up in a book. > > > > Thank you, > > > > Kevin > > > > Master of Science Student > > Department of Food, Resource and Agricultural Economics > > University of Guelph > Office: 519-824-4120 ext. 58528 > > Mobile: 226-979-2813 > > <http://fare.uoguelph.ca/users/kchang01> > http://fare.uoguelph.ca/users/kchang01 > > > > > > > [[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. -- Bert Gunter Genentech Nonclinical Biostatistics Internal Contact Info: Phone: 467-7374 Website: http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm ______________________________________________ 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.
