Inline
On 2012-07-17 04:16, MK wrote:
Hi,
How do I use the subset function without losing the attributes?
You don't. At least not without modifying subset.data.frame().
The key sentence on the ?Extract help page is this:
"Subsetting (except by an empty index) will drop all
attributes except names, dim and dimnames."
(This should probably say "... by an empty _first_ index ...")
If you really want a subset function to do what you want then
it's an easy modification; just replace the last line of
subset.data.frame with
if(isTRUE(r))
x[, vars, drop = drop]
else
x[r, vars, drop = drop]
But this still won't let you pick subsets of rows without
losing the attributes. So I see no advantage over [,].
I would just save the attributes and reassign them.
Peter Ehlers
For example,
test.df <- data.frame(a = rnorm(100), b = runif(100), c = rexp(100))
attr(test.df[, 1], "units") <- c("cm")
attr(test.df[, 2], "units") <- c("kg")
attr(test.df[, 3], "units") <- c("ha")
## We want this behavior
str(test.df[, "a", drop = FALSE])
## But not the behavior of subset
str(subset(test.df, select = a, drop = FALSE))
## Whic is equivalent to
str(test.df[TRUE, "a", drop = FALSE])
Cheers,
M