[Rd] colnames slow (PR#10470)

[Uwe Ligges]

tomas.larsson at gm.com wrote:
> Full_Name: Tomas Larsson
> Version: 2.6.0
> OS: Windows XP
> Submission from: (NULL) (198.208.251.24)
> 
> 
> This is not a bug, it is a performance issue but I think it should have an easy
> fix.
> 
> I have a large matrix (about 2,000,000 by 20), when I type colnames(x) it takes
> a long time to get the result.  However, if I select just the first couple of
> rows of the matrix I don't have to wait for the result. See below for example.
> 
>> system.time(colnames(x))
>    user  system elapsed 
>    9.98    0.00   10.00 
>> system.time(colnames(x[1:2,]))
>    user  system elapsed 
>    0.01    0.00    0.02 


Documentation in the released version of R (2.6.1) tells us:

For a data frame, 'rownames'
      and 'colnames' are calls to 'row.names' and 'names' respectively,
      but the latter are preferred.

and on my machine I get:

system.time(names(x))
    user  system elapsed
       0       0       0


Uwe Ligges



> Sincerely,
> 
> Tomas
> 
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