deepcopy appears to drops dimnames when `cols` argument used

[cdeterman]

Even when options(bigmemory.allow.dimnames = TRUE) it appears that deepcopy is dropping dimnames (notably column names) when you wish to subset the columns.

For example:

df <- data.frame(A = seq(2), B = rnorm(2))
bm <- as.big.matrix(df)
dm <- deepcopy(bm, cols = 1)

colnames(bm)
[1] "A" "B"

colnames(dm)
NULL

This is not the case though if the cols argument is not used:

dm <- deepcopy(bm)

colnames(bm)
[1] "A" "B"