[Rcpp-devel] Performance question about DataFrame

[John Merrill]

I agree that this is not a complete implementation; it isn't meant to be,
although it might still be a worth incorporating this into Rcpp with the
appropriate fixes in place.

For instance, the vector recycling issue is far from the greatest
limitation of this code: it handles character vectors wrong,  The R routine
converts character vectors into factors unless overridden; I wrote the
precursor of this particular routine because I wanted to handle strings
faithfully, and so writing a stupid R routine to coerce lists of lists of
constant length to data frames.


On Thu, Jan 31, 2013 at 3:21 AM, Romain Francois
<romain at r-enthusiasts.com>wrote:

> Le 15/01/13 16:20, John Merrill a écrit :
>
>  It appears that DataFrame::create is a thin layer on top of the R
>> data.frame call.  The guarantee correctness, but also means the
>> performance of an Rcpp routine which returns a large data frame is
>> limited by the performance of data.frame -- which is utterly horrible.
>>
>> In the current version of R, there's a trivial, but borderline evil,
>> work around: build a list of lists meeting the basic requirements of a
>> data frame (they all need to be of the same length, and each component
>> list needs to be named) and set the type of the object to "data.frame".
>>
>> I have two questions:
>> (1) Is it reasonable to anticipate that this hack will continue to work
>> for the near future in R?
>> (2) If so, would a patch to that effect be of interest to the developers?
>>
>
> The reason we used a callback to data.frame is close to lazyness on our
> part. With the R function, for example we know that columns of different
> sizes will be handled properly, with recylcling, etc ...
>
> Just making a named list of vectors is not enough. We have to make sure
> they all have the same length.
>
> Perhaps it would be worth checking this and make better DataFrame::create
> functions.
>
>
>
> Also, you can use a shortcut to assign row names, i.e. mimic this in C++
> (the second line contains the magic):
>
> > d <- list( x = 1:10, y = 1:10 )
> > attr( d, "row.names" ) <- c( NA, -10L )
> > attr( d, "class" ) <- "data.frame"
> > d
>     x  y
> 1   1  1
> 2   2  2
> 3   3  3
> 4   4  4
> 5   5  5
> 6   6  6
> 7   7  7
> 8   8  8
> 9   9  9
> 10 10 10
>
>
> Romain
>
> --
> Romain Francois
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