[R] Replace split with regex for speed ?

[rex.dwyer at syngenta.com]

That's a good solution, but if you're really, really sure that the timestamps are in the format you gave, it's quite a bit faster to use substr and paste, because you don't have to do any searching in the string.
HTH
Rex

> x = rep("09:30:00.000.633",1000000)
> system.time(y<-paste(substr(x,1,12),substr(x,14,16),sep=""))
   user  system elapsed
   0.87    0.00    0.88
> system.time(y<-sub("\\.(\\d+)$", "\\1", x))
   user  system elapsed
   1.65    0.00    1.65
> system.time(y<-sub("\\.(\\d+)$", "\\1", x))
   user  system elapsed
   1.65    0.00    1.66
> system.time(y<-paste(substr(x,1,12),substr(x,14,16),sep=""))
   user  system elapsed
   0.88    0.00    0.89
>

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Henrique Dallazuanna
Sent: Friday, March 18, 2011 8:32 AM
To: rivercode
Cc: r-help at r-project.org
Subject: Re: [R] Replace split with regex for speed ?

Try this:

 sub("\\.(\\d+)$", "\\1", ts)


On Thu, Mar 17, 2011 at 11:01 PM, rivercode <aquanyc at gmail.com> wrote:
>
> Have timestamp in format HH:MM:SS.MMM.UUU and need to remove the last "." so
> it is in format HH:MM:SS.MMMUUU.
>
> What is the fastest way to do this, since it has to be repeated on millions
> of rows. Should I use regex ?
>
> Currently doing it with a string split, which is slow:
>
>  >head(ts)
> [1]  09:30:00.000.245  09:30:00.000.256  09:30:00.000.633  09:30:00.001.309
> 09:30:00.003.635  09:30:00.026.370
>
>
>  ts = strsplit(ts, ".", fixed = TRUE)
>  ts=lapply(ts, function(x) { paste(x[1], ".", x[2], x[3], sep="") } )  #
> Remove last . from timestamp, from HH:MM:SS.MMM.UUU to HH:MM:SS.MMMUUU
>  ts = unlist(ts)
>
> Thanks,
> Chris
>
> --
> View this message in context: http://r.789695.n4.nabble.com/Replace-split-with-regex-for-speed-tp3386098p3386098.html
> Sent from the R help mailing list archive at Nabble.com.
>
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>



--
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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