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". > 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.
