[Rd] Varying as.Date performance

[Jeff Enos]

R-devel,

The performance of as.Date differs by a large degree between one of my
machines with glibc 2.3.2:

> system.time(x <- as.Date(rep("01-01-2005", 100000), format = "%m-%d-%Y"))
[1] 1.17 0.00 1.18 0.00 0.00

and a comparable machine with glibc 2.3.3:

> system.time(x <- as.Date(rep("01-01-2005", 100000), format = "%m-%d-%Y"))
[1] 31.20 46.89 81.01  0.00  0.00

both with the same R version:

> R.version
         _                
platform i686-pc-linux-gnu
arch     i686             
os       linux-gnu        
system   i686, linux-gnu  
status                    
major    2                
minor    1.0              
year     2005             
month    04               
day      18               
language R

I'm focusing on differences in glibc versions because of as.Date's use
of strptime.

Does it seem likely that the cause of this discrepancy is in fact
glibc?  If so, can anyone tell me how to make the performance of the
second machine more like the first?

I have verified that using the chron package, which I don't believe
uses strptime, for the above character conversion performs equally
well on both machines.

Thanks in advance,

Jeff