[datatable-help] can I count on data.table supporting syntactically invalid column names?

[Matthew Dowle]

Hi. Yes you should be able to rely on that. It's useful to have special
characters in column names for latex formatting, and spaces are allowed
too. There are tests for these things. If you need to refer to such column
names as variables, then it's up to you to wrap with ``; e.g.,
by=`Illegal(name%)`+1.

If you find problems please report as bugs, and suggest where the
documentation needs improving would be great.

I seem to remember a bug fix in this regard, and in particular in merge
(so my first thought is to ask you if you've recently upgraded to 1.8.2
and if test.data.table returns 717), but as you say R-Forge is currently
down for maintenance...

That neworder error looks familiar too. Are you sure you have 1.8.2
running in memory? (Run test.data.table() to see if it returns 717).

Matthew

> I'm taking advantage of a feature in data.table which lets me get away
> with naming columns with characters that would not survive a call to
> make.names(), e.g.:
>
>> DT1 = data.table(a=letters[1:5], "Illegal(name%)"=1:5, key="a")
>> DT1
>    a Illegal(name%)
> 1: a              1
> 2: b              2
> 3: c              3
> 4: d              4
> 5: e              5
>
> (The the dcast function from the reshape2 package will also create columns
> named "illegally".)
>
> But when using merge.data.table, I get two side-effects; either the merge
> works, but the column names appear to be run through make.names(), or the
> merge fails in setcolorder():
>
>> DT1 = data.table(a=letters[1:5], "Illegal(name%)"=1:5, key="a")
>> DT2 = data.table(a=letters[1:5], b=6L, key="a")
>
>> merge(DT1,DT2)
>    a Illegal.name.. b
> 1: a              1 6
> 2: b              2 6
> 3: c              3 6
> 4: d              4 6
> 5: e              5 6
>
>> merge(DT2,DT1)
> Error in setcolorder(dt, c(setdiff(names(dt), end), end)) :
>   neworder is length 4 but x has 3 columns.
>
> I can't get to datatable.r-forge.r-project.org - getting a 504.
>
> So... should I NOT rely on being able to use special characters in column
> names?
>
> Thanks
> George
>
>> sessionInfo()
> R version 2.15.0 (2012-03-30)
> Platform: x86_64-unknown-linux-gnu (64-bit)
> [1] data.table_1.8.2
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