[Rd] colnames for data.frame could be greatly improved

[Jan Gorecki]

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