On Jun 10, 2015, at 12:18 PM, David Winsemius wrote: > > On Jun 10, 2015, at 5:39 AM, Liz Hare wrote: > >> Hi R-Experts, >> >> I have a data.frame like this: >> >>> head(map) >> chr snp poscm posbp dist >> 1 1 M1 2.99043 3249189 NA >> 2 1 M2 3.06457 3273096 0.07414 >> 3 1 M3 3.17018 3307151 0.10561 >> 4 1 M4 3.20892 3319643 0.03874 >> 5 1 M5 3.28120 3342947 0.07228 >> 6 1 M6 3.29624 3347798 0.01504 >> >> I need to split this into chunks of 250 rows (there will usually be a last >> chunk with < 250 rows). > > split( map, trunc( 0:(nrow(map)-1 )/nrow(map) ) ) > > Untested. Designed to return a list with indices starting at "0".
Looking at Marc Schwartz' answer ( a smarter man than I) I see this should have been: split( map, trunc( 0:(nrow(map)-1 )/250) ) -- David. > >> trunc( 0:19/5) > [1] 0 0 0 0 0 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 > > > >> >> If I only had to extract one 250-line chunk, it would be easy: >> >> map1 <- map[1:250, ] >> >> or using subset(). >> >> I tried to make it a loop iterating through num and using beg and nd for >> starting and ending indices, but I couldn’t figure out how to reference all >> the variables I needed in this: >> >>> chunks >> beg nd let num >> 1 1 250 a 1 >> 2 251 500 b 2 >> 3 501 750 c 3 >> 4 751 1000 d 4 >> 5 1001 1250 e 5 >> 6 1251 1500 f 6 >> 7 1501 1750 g 7 >> 8 1751 2000 h 8 >> 9 2001 2250 i 9 >> 10 2251 2500 j 10 >> … >> >> Remembering that loops are not always the best answer in R, I looked at >> other options like split, following this example but not being able to adapt >> it from a vector to a data.frame version >> http://stackoverflow.com/questions/3318333/split-a-vector-into-chunks-in-r >> <http://stackoverflow.com/questions/3318333/split-a-vector-into-chunks-in-r> >> (Yes, I’ve reviewed the language documentation). I checked out ddply and >> data.table, but couldn’t find a way to use them with index positions instead >> of column values. >> >> Thanks, >> Liz >> >> >> >> [[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. > > David Winsemius > Alameda, CA, USA > > ______________________________________________ > 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. David Winsemius Alameda, CA, USA ______________________________________________ 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.
