Hi Joseph, Fixed, in 1.5.2 i.e. the ugly double eval no longer needed. Just eval the parse()-ed expression with no need for the quote(). Thanks for finding this one. Matthew
On Sun, 2011-01-02 at 08:21 +0000, Matthew Dowle wrote: > Thanks again. Yes looks like a bug. Added here : > https://r-forge.r-project.org/tracker/index.php?func=detail&aid=1243&group_id=240&atid=975 > Matthew > > On Fri, 2010-12-31 at 17:10 -0500, Joseph Voelkel wrote: > > Matthew, just to address point 5 (double eval of quoted works, single eval > > on unquoted does not): > > > > > dt1key<-data.table(A1=1:100,onekey=rep(1:2,each=50)) > > > setkey(dt1key,onekey) > > > ASumExpr<-parse(text="quote(sum(A1))") > > > ASumExpr > > expression(quote(sum(A1))) > > attr(,"srcfile") > > <text> > > > str(eval(ASumExpr)) > > language sum(A1) > > > > > > ASumExprNoQ<-parse(text="sum(A1)") > > > ASumExprNoQ > > expression(sum(A1)) > > attr(,"srcfile") > > <text> > > > str(ASumExprNoQ) # not the same as eval(ASumExpr) > > length 1 expression(sum(A1)) > > - attr(*, "srcref")=List of 1 > > ..$ :Class 'srcref' atomic [1:6] 1 1 1 7 1 7 > > .. .. ..- attr(*, "srcfile")=Classes 'srcfilecopy', 'srcfile' > > <environment: 0x060cef18> > > - attr(*, "srcfile")=Classes 'srcfilecopy', 'srcfile' <environment: > > 0x060cef18> > > > > > > # test of 3 ways to obtain results > > > dt1key[,sum(A1),by=onekey] > > onekey V1 > > [1,] 1 1275 > > [2,] 2 3775 > > > dt1key[,eval(eval(ASumExpr)),by=onekey] > > onekey V1 > > [1,] 1 1275 > > [2,] 2 3775 > > > dt1key[,eval(ASumExprNoQ),by=onekey] > > Error in `[.data.table`(dt1key, , eval(ASumExprNoQ), by = onekey) : > > columns of j don't evaluate to consistent types for each group > > In addition: Warning message: > > In if (as.character(jsub[[1]]) %in% c("list", "DT")) { : > > the condition has length > 1 and only the first element will be used > > > > > > > > > > -----Original Message----- > > From: Matthew Dowle [mailto:[email protected]] On Behalf Of > > Matthew Dowle > > Sent: Friday, December 31, 2010 9:13 AM > > To: Joseph Voelkel > > Cc: [email protected] > > Subject: RE: [datatable-help] Summing over many variables > > > > Hi, > > > > I don't quite follow all of that e.g. I'm thinking secondary keys at > > points (manual now, or 'built-in' feature request). Anyway, sounds like > > it's working. On point 3 I'm not sure that's really data.table, rather > > the difference between a vectorized sum and apply()-ed sum. You should > > see the same difference with a data.frame. > > > > Where it isn't working (point 5) was there an error message or was the > > result incorrect? Might be a clue that reveals a bug. > > > > Matthew > > > > On Wed, 2010-12-29 at 12:57 -0500, Joseph Voelkel wrote: > > > Thanks, Matthew. > > > > > > 1. Yes, you have the subsetting of j on your faq. > > > 2. The double eval appears to handle this subsetting. In my smaller > > > problem, which I am working on first, I have about 55K records and 250 > > > variables. Using either A1+A2+A3+A4+A5 or eval(eval()) takes about 0.22 > > > sec of user time. So, from this indirect measure, the two are equally > > > efficient. > > > 3. By the way, for this example, I used 6 keys, which happened for this > > > problem to correspond to 1 record for each unique key. That is, my output > > > also contained 55K records. I originally solved the problem by using > > > apply with sum on the five columns that contained the A1 through A5 > > > value, e.g. apply(DT1[,11:15,with=FALSE],1,sum). This operation took > > > about 0.62 sec. So, even here, data.table is 3x faster than apply. > > > 4. Of course, no key is really needed here, so if I just want to return > > > the sum along with the key vars, I can just use > > > DT1[,list(key1,key2,key3,key4,key5,key6,sum=A1+A2+A3+A4+A5)] which runs > > > in under 0.01 seconds. > > > 5. Finally, I tried your idea of removing the quote and just trying the > > > one eval(). It worked with a simple contrived example, but not for my > > > more complex one--I have no idea why not, because the two seem > > > analogous... > > > > > > > > > > > > -----Original Message----- > > > From: Matthew Dowle [mailto:[email protected]] On Behalf Of > > > Matthew Dowle > > > Sent: Tuesday, December 28, 2010 12:22 PM > > > To: Joseph Voelkel > > > Cc: [email protected] > > > Subject: Re: [datatable-help] Summing over many variables > > > > > > Glad that works. Thanks for posting back. One thintg with that approach > > > is that data.table inspects the j expression to see which columns it > > > uses. It only subsets the ones that are used, for efficiency. There's a > > > faq on that I think. If the expression is wrapped up inside an eval I > > > think it still inspects the j but I can't quite remember. I'd be > > > surprised if that works with the double eval like that. If A runs from 1 > > > to 100 in your real data and you're taking many sub-sums of 5, then this > > > could make a big difference. Try timing sum(A1) vs sum(A2+A3+A4+A5) with > > > and without the eval(eval()). That should reveal whether the j is being > > > inspected ok. > > > Also looking at it again, you shouldn't need the quote() inside the text > > > passed to parse. Then it's just a single eval and j inspection should be > > > ok I think i.e. DT1[,eval(ASumExpr),by=grp] rather than > > > DT1[,eval(eval(ASumExpr)),by=grp] > > > > > > Matthew > > > > > > > > > On Mon, 2010-12-27 at 13:23 -0500, Joseph Voelkel wrote: > > > > I like Matthew's idea of flattening tables. But, as usual, I did not > > > > tell the whole story in my first post. I will probably want to look at > > > > many expressions, for example, > > > > > > > > sum(A1+A2+A3+A4+A5) > > > > sum(A2+A3+A4+A5+A6) > > > > sum(A3+A4+A5+A6+A7) > > > > sum((A1+A2)/2 - (A3+A4)/2) > > > > > > > > To be able to investigate a sequence of these easily, I found (after > > > > some trial and error, and then thinking about it a bit more to try to > > > > make my problem look like one from the datatable-faq) that this will do > > > > the trick: > > > > > > > > library(data.table) > > > > > > > > # create data table > > > > DT1<-data.table(A1=1:1000000,A2=1:1000000,A3=1:1000000,A4=1:1000000,A5=1:1000000,grp=rep(1:50000,each=20)) > > > > setkey(DT1,grp) > > > > > > > > # Say I want DT1[,sum(A1+A2+A3+A4+A5),by=grp] > > > > > > > > # First, create expression of interest, and convert it to > > > > data-table-useful form > > > > ASumExpr<-parse(text=paste("quote(sum(",paste("A",1:5,sep="",collapse="+"),"))",sep="")) > > > > # (Next few lines: to help me and maybe you see what this looks like...) > > > > ASumExpr > > > > str(ASumExpr) > > > > eval(ASumExpr) > > > > str(eval(ASumExpr)) > > > > str(quote(mean(x))) # from example in datatable-faq.pdf. So > > > > eval(ASumExpr) looks good > > > > > > > > # long-hand typing method. OK for one or two, but not in general > > > > system.time(dt2a<-DT1[,sum(A1+A2+A3+A4+A5),by=grp]) > > > > # formula method. This will be useful. > > > > system.time(dt2b<-DT1[,eval(eval(ASumExpr)),by=grp]) > > > > > > > > identical(dt2a, dt2b) > > > > > > > > # Fast and easy to write. Just what I wanted. Thanks again for the > > > > ideas that lead to this useful solution. > > > > > > > > Joe V. > > > > > > > > -----Original Message----- > > > > From: Matthew Dowle [mailto:[email protected]] On Behalf Of > > > > Matthew Dowle > > > > Sent: Thursday, December 23, 2010 4:33 PM > > > > To: Joseph Voelkel > > > > Cc: [email protected] > > > > Subject: Re: [datatable-help] Summing over many variables > > > > > > > > > > > > Yes that's one way. We aren't that happy with using lapply in j as it > > > > loses the benefit of data.table. > > > > > > > > I tend to 'flatten' tables like this. Try to have few columns. In this > > > > case it would be either a 3 column table (grp,colname,value) or maybe a > > > > 4 column table if you ever want to group by "A" or > > > > "B" (grp,letter,number,value). The query would then be > > > > DT[,sum(value),by=list(grp,letter,number)]. You can then do pattern > > > > matches and filters etc in the i rather than in the j e.g. > > > > DT[letter=="A",sum(value),by=group] for just the "A"s. The answer comes > > > > out in 'flat' format but you can always 'unflatten' the result to make > > > > it look pretty or easier to read. [Note that I sinned by using '==' in > > > > the i just then invoking vector scan, so to avoid that for speed you > > > > would setkey(letter,group) then DT["A",sum(value),by=group]], or getting > > > > fancy if you only wanted some groups (say 1 and 3) then 'by without by' > > > > e.g. DT[list("A",c(1,3)),sum(value)]. > > > > > > > > 'flat' is a common way to use data.table to store higher dimensional > > > > data, and especially sparse higher dimensional data. > > > > > > > > The 'grp.1' repetition is a problem I'd like to remove. It's related to > > > > this feature request (but is almost a bug). At the moment you have to > > > > remove the grp.1 afterwards. > > > > https://r-forge.r-project.org/tracker/index.php?func=detail&aid=978&group_id=240&atid=978 > > > > > > > > Matthew > > > > > > > > _______________________________________________ > > > > 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 _______________________________________________ datatable-help mailing list [email protected] https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
