Hi. A quick read suggests it's not intended and that's a bug. Just convert the columns to character for now, and it should work. Character columns are now preferred going forward, so I'd be suggesting that anyway even if it worked.
> So in case this is expected behavior, should data.table > give at least a warning that says something like "You join two > data.tables whereby one keyed column is a factor, one is a character. > That is probably not your intention. Convert the factor column to > character or vice versa."? Yes. It should be converting to character (with a warning) in this case. Thought that's what I coded and tested. Will investigate... > Hi together, > > here is the problem I needed dput for: http://www.fileuploadx.de/287440 > (sorry, > I know that this filehoster is annoying because you have to wait until you > can download the file; I hope you have a coffee machine close by ;-) > > In this attachment, I basically load in two data.tables DT1 and DT2 that I > want to join, i.e. DT2[DT1], according to the keyed columns "Company_Code" > and "intDatum" in DT1 and "DSCD" and "intDatum" in DT2. However, while > "DSCD" is formatted as a character-column, "Company_Code" is formatted as > a > factor-column. As you can see from the long structure-object, there are > plenty of levels here (the actual data.tables are very small). > > Now, when I try to join those with DT2[DT1], I get: > > > DSCD intDatum MONTH MV SICClass > [1,] 997859 151 <NA> NA 44 > [2,] 997859 152 <NA> NA 44 > [3,] 998064 151 <NA> NA 15 > [4,] 998064 152 <NA> NA 15 > [5,] 142268 151 <NA> NA 53 > [6,] 142268 152 <NA> NA 53 > [7,] 142859 151 <NA> NA 56 > [8,] 142859 152 <NA> NA 56 > [9,] 143415 151 <NA> NA 63 > [10,] 143415 152 <NA> NA 63 > [11,] 307045 151 <NA> NA 15 > [12,] 307045 152 <NA> NA 15 > > > > Basically, data.table finds no values for MV and MONTH for any DSCD > and intDatum combination. However, as DT2[DSCD=="142268"] clearly > shows, there are values for that DSCD: > > > > DSCD MONTH MV intDatum > [1,] 142268 1997-08-28 1901.12 151 > [2,] 142268 1997-09-28 1829.00 152 > > > > Those, however, only show up in the join after i get rid of all the > unused levels (equivalently, I can also transform the Company_Code to > a character column): > > > DT1[, Company_Code := factor(Company_Code)] > DT2[DT1] > > > DSCD intDatum MONTH MV SICClass > [1,] 997859 151 <NA> NA 44 > [2,] 997859 152 <NA> NA 44 > [3,] 998064 151 <NA> NA 15 > [4,] 998064 152 <NA> NA 15 > [5,] 142268 151 1997-08-28 1901.12 53 > [6,] 142268 152 1997-09-28 1829.00 53 > [7,] 142859 151 <NA> NA 56 > [8,] 142859 152 <NA> NA 56 > [9,] 143415 151 <NA> NA 63 > [10,] 143415 152 <NA> NA 63 > [11,] 307045 151 <NA> NA 15 > [12,] 307045 152 <NA> NA 15 > > > > I'm pretty sure this behaviour occurred only with version 1.8.0, > probably because data.table coerced every key to factor before (see > the NEWS to 1.8.0). So my question is: Is what happens here intended > behavior? I'm honest with you: I'm working now for a while with R and > factors are one of those things that I never got. I just don't see > their use and every so often they cause me huge problems (as in this > case). So I'm probably making something stupid here. The nasty thing > about this issue here is that mostly, however, the joins just work as > expected (believe me, I tried to produce a simple example with one > column factor and one character that would reproduce this behavior, > but no matter what I did, the joins afterwards always worked as > expected). So in case this is expected behavior, should data.table > give at least a warning that says something like "You join two > data.tables whereby one keyed column is a factor, one is a character. > That is probably not your intention. Convert the factor column to > character or vice versa."? > > > > Thanks for your help! > > > > Christoph > _______________________________________________ > datatable-help mailing list > [email protected] > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help _______________________________________________ datatable-help mailing list [email protected] https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
