[R] please comment on my function

[jim holtman]

First thing to do is to run Rprof and see where the time is going;
here it is from my computer:

                      self.time self.pct total.time total.pct
tolower                    4.42    39.46       4.42     39.46
sub                        3.56    31.79       3.56     31.79
nchar                      1.54    13.75       1.54     13.75
canonicalize.language      0.62     5.54      11.14     99.46
!=                         0.52     4.64       0.52      4.64
==                         0.26     2.32       0.26      2.32
&                          0.22     1.96       0.22      1.96
gc                         0.06     0.54       0.06      0.54

more than half the time is in 'tolower' and 'nchar', so it is not all
'sub's problem.

This version runs a little faster since it does not need the 'tolower':

canonicalize.language <- function (s) {
  # s <- tolower(s)
  long <- nchar(s) == 5
  s[long] <- sub("^([[:alpha:]]{2})[-_][[:alpha:]]{2}$","\\1",s[long])
  s[nchar(s) != 2 & s != "c"] <- "unknown"
  s
}


On Fri, Sep 14, 2012 at 12:30 PM, Sam Steingold <sds at gnu.org> wrote:
> this function is supposed to canonicalize the language:
>
> --8<---------------cut here---------------start------------->8---
> canonicalize.language <- function (s) {
>   s <- tolower(s)
>   long <- nchar(s) == 5
>   s[long] <- sub("^([a-z]{2})[-_][a-z]{2}$","\\1",s[long])
>   s[nchar(s) != 2 & s != "c"] <- "unknown"
>   s
> }
> canonicalize.language(c("aa","bb-cc","DD-abc","eee","ff_FF","C"))
> [1] "aa"      "bb"      "unknown" "unknown" "ff"      "c"
> --8<---------------cut here---------------end--------------->8---
>
> it does what I want it to do, but it takes 4.5 seconds on a vector of
> length 10,256,341 - I wonder if I might be doing something aufully stupid.
> I thought that sub() was slow, but my second attempt:
> --8<---------------cut here---------------start------------->8---
> canonicalize.language <- function (s) {
>   s <- tolower(s)
>   good <- nchar(s) == 5 & substr(s,3,3) %in% c("_","-")
>   s[good] <- substr(s[good],1,2)
>   s[nchar(s) != 2 & s != "c"] <- "unknown"
>   s
> }
> --8<---------------cut here---------------end--------------->8---
> was even slower (6.4 sec).
>
> My two concerns are:
>
> 1. avoid allocating many small objects which are never collected
> 2. run fast
>
> Which would be the best implementation?
>
> Thanks a lot for your insight!
>
> --
> Sam Steingold (http://sds.podval.org/) on Ubuntu 12.04 (precise) X 11.0.11103000
> http://www.childpsy.net/ http://think-israel.org http://openvotingconsortium.org
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>
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-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.