On 05/04/2014 1:10 PM, Dan Murphy wrote:
Thanks, Duncan. Using names is certainly the most reliable solution,
but requires remembering to modify the "surrounding code" when
enhancing what's within -- a bug risk source when passing on the code.
Are you saying that an automatic reversal as follows may break in the
future because R-devel may change the current behavior of 'within'?
I'm saying that there might already be cases where that code breaks.
(If so, then that's the greater source of bug risk .. so back to
'names'.)
ln <- length(foo)
foo <- within(foo, {
bar <- whatever
other()
})
foo <- foo[c(1:ln, length(foo):(ln+1))] # to reverse within's assumed
backwards column order
Is there a way to capture the names of new objects created within?
Sure, something ike this should work:
oldvars <- names(foo)
foo <- within(foo, {...})
newvars <- setdiff(names(foo), oldvars)
There might also be changes to the oldvars; within doesn't just add
columns, it can modify existing ones.
Duncan Murdoch
On Fri, Apr 4, 2014 at 10:55 AM, Duncan Murdoch
<murdoch.dun...@gmail.com> wrote:
> On 04/04/2014 1:32 PM, Dan Murphy wrote:
>>
>> I just noticed this annoyance, but I'm not the first one, apparently
>> -- see
>>
http://lists.r-forge.r-project.org/pipermail/datatable-help/2012-May/001176.html
>>
>> The thread never answered the OP's question "Is this a bug?" so I
>> assume the answer, unfortunately, is No.
>>
>> If not a bug, do users of within have a workaround to produce a result
>> with columns as ordered within 'within'? I can think of a way using
>> names and subset-with-select, but that seems unduly kludgy.
>
>
> I wouldn't be surprised if it is not consistent about that. It uses as.list
> to convert an environment to a list, and that's where the reversal occurs:
> but since environments are unordered collections of objects, you just happen
> to be seeing an undocumented and unpromised property of the internal
> implementation.
>
> If the order matters to you, then create your initial dataframe with the new
> variables (set to NA, for example), or reorder it afterwards. But generally
> speaking even in a dataframe (which is an ordered collection of objects),
> it's better to program in a way that doesn't make assumptions about the
> order. Columns have names, and you should use those.
>
> Duncan Murdoch
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
