Hello, colnames seems to be not optimized well for data.frame. It escapes processing for data.frame in
if (is.data.frame(x) && do.NULL) return(names(x)) but only when do.NULL true. This makes huge difference when do.NULL false. Minimal edit to `colnames`: if (is.data.frame(x)) { nm <- names(x) if (do.NULL || !is.null(nm)) return(nm) else return(paste0(prefix, seq_along(x))) } Script and timings: N=1e7; K=100 set.seed(1) DF <- data.frame( id1 = sample(sprintf("id%03d",1:K), N, TRUE), # large groups (char) id2 = sample(sprintf("id%03d",1:K), N, TRUE), # large groups (char) id3 = sample(sprintf("id%010d",1:(N/K)), N, TRUE), # small groups (char) id4 = sample(K, N, TRUE), # large groups (int) id5 = sample(K, N, TRUE), # large groups (int) id6 = sample(N/K, N, TRUE), # small groups (int) v1 = sample(5, N, TRUE), # int in range [1,5] v2 = sample(5, N, TRUE), # int in range [1,5] v3 = sample(round(runif(100,max=100),4), N, TRUE) # numeric e.g. 23.5749 ) cat("GB =", round(sum(gc()[,2])/1024, 3), "\n") #GB = 0.397 colnames(DF) = NULL system.time(nm1<-colnames(DF, FALSE)) # user system elapsed # 22.158 0.299 22.498 print(nm1) #[1] "col1" "col2" "col3" "col4" "col5" "col6" "col7" "col8" "col9" ### restart R colnames <- function (x, do.NULL = TRUE, prefix = "col") { if (is.data.frame(x)) { nm <- names(x) if (do.NULL || !is.null(nm)) return(nm) else return(paste0(prefix, seq_along(x))) } dn <- dimnames(x) if (!is.null(dn[[2L]])) dn[[2L]] else { nc <- NCOL(x) if (do.NULL) NULL else if (nc > 0L) paste0(prefix, seq_len(nc)) else character() } } N=1e7; K=100 set.seed(1) DF <- data.frame( id1 = sample(sprintf("id%03d",1:K), N, TRUE), # large groups (char) id2 = sample(sprintf("id%03d",1:K), N, TRUE), # large groups (char) id3 = sample(sprintf("id%010d",1:(N/K)), N, TRUE), # small groups (char) id4 = sample(K, N, TRUE), # large groups (int) id5 = sample(K, N, TRUE), # large groups (int) id6 = sample(N/K, N, TRUE), # small groups (int) v1 = sample(5, N, TRUE), # int in range [1,5] v2 = sample(5, N, TRUE), # int in range [1,5] v3 = sample(round(runif(100,max=100),4), N, TRUE) # numeric e.g. 23.5749 ) cat("GB =", round(sum(gc()[,2])/1024, 3), "\n") #GB = 0.397 colnames(DF) = NULL system.time(nm1<-colnames(DF, FALSE)) # user system elapsed # 0.001 0.000 0.000 print(nm1) #[1] "col1" "col2" "col3" "col4" "col5" "col6" "col7" "col8" "col9" sessionInfo() #R Under development (unstable) (2016-12-19 r71815) #Platform: x86_64-pc-linux-gnu (64-bit) #Running under: Debian GNU/Linux stretch/sid # #locale: # [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C # [3] LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8 # [5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8 # [7] LC_PAPER=en_US.UTF-8 LC_NAME=C # [9] LC_ADDRESS=C LC_TELEPHONE=C #[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C # #attached base packages: #[1] stats graphics grDevices utils datasets methods base # # #loaded via a namespace (and not attached): #[1] compiler_3.4.0 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel