[R] Bug in "transform"?

[Prof Brian Ripley]

On Tue, 2 Dec 2008, Peter Dalgaard wrote:

> Prof Brian Ripley wrote:
>> As the help page says
>>
>>      If some of the values are not vectors of the appropriate length,
>>      you deserve whatever you get!
>
> Yes (did I write that?). It is a bit annoying with things that almost work, 
> though.
>
>
> [snip]
>> 
>>> I often need to use this for creating new variables in data frame from 
>>> those already present.
>>> Sorely needed!!
>> 
>> Just learn to use indexing: transform() is just syntactic sugar that you 
>> are not making use of.
>> 
>
> ...at least when you're not making use of the scoping aspects. And if you 
> calculate at least one vector of full length, then the issue goes away.
>
>
>
>> transform(aq, a=1,b=2)
> Error in data.frame(`_data`, e[!matched]) :
>  arguments imply differing number of rows: 6, 1
>> transform(aq, a=1,b=2,o=Ozone)
>    Ozone Solar.R Wind Temp Month Day a b  o
> 3      12     149 12.6   74     5   3 1 2 12
> 31     37     279  7.4   76     5  31 1 2 37
> 34     NA     242 16.1   67     6   3 1 2 NA
> 65     NA     101 10.9   84     7   4 1 2 NA
> 59     NA      98 11.5   80     6  28 1 2 NA
> 133    24     259  9.7   73     9  10 1 2 24
>
>
>
> The underlying issue is actually not in transform() but in data.frame():

Well, no, it is in the way that you call data.frame().  If you want to add 
several variables, pass them as separate arguments rather than as a list 
(just as they were passed to transform.data.frame).  That's a simple 
change and will make transform.data.frame behave more consistently with 
cbind.data.frame and data.frame.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595