[R] subsetting without losing the attributes
ruipbarradas at sapo.pt
Wed Jul 18 09:23:55 CEST 2012
Another quote from the help pages that could be usefull is, from ?subset,
This is a convenience function intended for use interactively. For
programming it is better to use the standard subsetting functions like
[, and in particular the non-standard evaluation of argument subset can
have unanticipated consequences.
So if the op wants a behavior that can be seen with `[`, use the
recommended extractor function.
Hope this helps,
Em 18-07-2012 01:03, Peter Ehlers escreveu:
> On 2012-07-17 04:16, MK wrote:
>> 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
> x[, vars, drop = drop]
> 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])
>> R-help at r-project.org mailing list
>> PLEASE do read the posting guide
>> and provide commented, minimal, self-contained, reproducible code.
> R-help at r-project.org mailing list
> PLEASE do read the posting guide
> and provide commented, minimal, self-contained, reproducible code.
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