R devel - Jan 2012 - names<- appears to copy 3 times?

Hi,

$ R --vanilla
R version 2.14.1 (2011-12-22)
Platform: i686-pc-linux-gnu (32-bit)
> DF = data.frame(a=1:3,b=4:6)
> DF
  a b
1 1 4
2 2 5
3 3 6
> tracemem(DF)
[1] "<0x8898098>"
> names(DF)[2]="B"
tracemem[0x8898098 -> 0x8763e18]: 
tracemem[0x8763e18 -> 0x8766be8]: 
tracemem[0x8766be8 -> 0x8766b68]: 
> DF
  a B
1 1 4
2 2 5
3 3 6
> 
Are those 3 copies really taking place? 

Matthew

On Tue, Jan 17, 2012 at 9:11 PM, Matthew Dowle <mdowle at mdowle.plus.com>
wrote:
> Hi,
>
> $ R --vanilla
> R version 2.14.1 (2011-12-22)
> Platform: i686-pc-linux-gnu (32-bit)
>> DF = data.frame(a=1:3,b=4:6)
>> DF
> ?a b
> 1 1 4
> 2 2 5
> 3 3 6
>> tracemem(DF)
> [1] "<0x8898098>"
>> names(DF)[2]="B"
> tracemem[0x8898098 -> 0x8763e18]:
> tracemem[0x8763e18 -> 0x8766be8]:
> tracemem[0x8766be8 -> 0x8766b68]:
>> DF
> ?a B
> 1 1 4
> 2 2 5
> 3 3 6
>>
>
> Are those 3 copies really taking place?
>
tracemem() isn't likely to give false positives.  Since you're on
Linux, you could check by running under gdb and setting a breakpoint
on memtrace_report, which is the function that prints the message.
That would show where the duplicates are happening.

  - thomas

-- 
Thomas Lumley
Professor of Biostatistics
University of Auckland