sorting a data.frame using a vector
"Liaw, Andy" <andy_liaw at merck.com> writes:
But I'm not happy with it because it is not really efficient. Any other suggestions are welcome!
Anything wrong with x[y,] ???
Well... sometimes:
nm <- as.character(sample(1:1e5)) x <- data.frame(x1=rnorm(1e5), row.names=1:1e5) system.time(x[nm, , drop=FALSE], gcFirst=TRUE)
[1] 155.13 0.01 156.10 NA NA
system.time(x2<-x[match(nm, rownames(x)), , drop=FALSE], gcFirst=TRUE)
[1] 0.37 0.00 0.37 NA NA
all(rownames(x2) == nm)
[1] TRUE
Yes, the internals are using pmatch(i, rows, duplicates.ok = TRUE) and pmatch() is a horrible lot slower than match(). Anyone for a spot of hardcore optimization? (Partial matching of character indices is a feature long regretted by its inventors, but every time we consider killing it, we tend to recoil in horror upon realizing what it would break...)
O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907