You could define functions like is.true <- function(x) !is.na(x) & x is.false <- function(x) !is.na(x) & !x and use them in your selections. E.g., > x <- data.frame(a=1:10,b=2:11,c=c(1,NA,3,NA,5,NA,7,NA,NA,10)) > x[is.true(x$c >= 6), ] a b c 7 7 8 7 10 10 11 10
Bill Dunlap TIBCO Software wdunlap tibco.com On Fri, Feb 27, 2015 at 7:27 AM, Dimitri Liakhovitski < dimitri.liakhovit...@gmail.com> wrote: > Thank you very much, Duncan. > All this being said: > > What would you say is the most elegant and most safe way to solve such > a seemingly simple task? > > Thank you! > > On Fri, Feb 27, 2015 at 10:02 AM, Duncan Murdoch > <murdoch.dun...@gmail.com> wrote: > > On 27/02/2015 9:49 AM, Dimitri Liakhovitski wrote: > >> So, Duncan, do I understand you correctly: > >> > >> When I use x$x<6, R doesn't know if it's TRUE or FALSE, so it returns > >> a logical value of NA. > > > > Yes, when x$x is NA. (Though I think you meant x$c.) > > > >> When this logical value is applied to a row, the R says: hell, I don't > >> know if I should keep it or not, so, just in case, I am going to keep > >> it, but I'll replace all the values in this row with NAs? > > > > Yes. Indexing with a logical NA is probably a mistake, and this is one > > way to signal it without actually triggering a warning or error. > > > > BTW, I should have mentioned that the example where you indexed using > > -which(x$c>=6) is a bad idea: if none of the entries were 6 or more, > > this would be indexing with an empty vector, and you'd get nothing, not > > everything. > > > > Duncan Murdoch > > > > > >> > >> On Fri, Feb 27, 2015 at 9:13 AM, Duncan Murdoch > >> <murdoch.dun...@gmail.com> wrote: > >>> On 27/02/2015 9:04 AM, Dimitri Liakhovitski wrote: > >>>> I know how to get the output I need, but I would benefit from an > >>>> explanation why R behaves the way it does. > >>>> > >>>> # I have a data frame x: > >>>> x = data.frame(a=1:10,b=2:11,c=c(1,NA,3,NA,5,NA,7,NA,NA,10)) > >>>> x > >>>> # I want to toss rows in x that contain values >=6. But I don't want > >>>> to toss my NAs there. > >>>> > >>>> subset(x,c<6) # Works correctly, but removes NAs in c, understand why > >>>> x[which(x$c<6),] # Works correctly, but removes NAs in c, understand > why > >>>> x[-which(x$c>=6),] # output I need > >>>> > >>>> # Here is my question: why does the following line replace the values > >>>> of all rows that contain an NA # in x$c with NAs? > >>>> > >>>> x[x$c<6,] # Leaves rows with c=NA, but makes the whole row an NA. > Why??? > >>>> x[(x$c<6) | is.na(x$c),] # output I need - I have to be > super-explicit > >>>> > >>>> Thank you very much! > >>> > >>> Most of your examples (except the ones using which()) are doing logical > >>> indexing. In logical indexing, TRUE keeps a line, FALSE drops the > line, > >>> and NA returns NA. Since "x$c < 6" is NA if x$c is NA, you get the > >>> third kind of indexing. > >>> > >>> Your last example works because in the cases where x$c is NA, it > >>> evaluates NA | TRUE, and that evaluates to TRUE. In the cases where > x$c > >>> is not NA, you get x$c < 6 | FALSE, and that's the same as x$c < 6, > >>> which will be either TRUE or FALSE. > >>> > >>> Duncan Murdoch > >>> > >> > >> > >> > > > > > > -- > Dimitri Liakhovitski > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.