[R] Is it possible to remove this loop? [SEC=UNCLASSIFIED]

[Pascal Oettli]

Le 04/07/2012 12:43, Peter Ehlers a écrit :
> On 2012-07-03 17:23, Jin.Li at ga.gov.au wrote:
>> Thank you all for providing various alternatives. They are all pretty
>> fast. Great help! Based on a test of a dataset with 800,000 rows, the
>> time used varies from 0.04 to 11.56 s. The champion is:
>>> a1$h2 <- 0
>>> a1$h2[a1$h1=="H"] <- 1
>
> Interesting. My testing shows that Petr's solution is about
> twice as fast. Not that it matters much - the time is pretty
> small in any case.
>
>   a0 <- data.frame(h1 = sample(c("H","J","K"), 1e7, replace = TRUE),
>                    stringsAsFactors = FALSE)
>   a1 <- a0
>   system.time({a1$h2 <- 0; a1$h2[a1$h1 == "H"] <- 1})
>   #   user  system elapsed
>   #   1.47    0.48    1.96
>   a11 <- a1
>
>   a1 <- a0
>   system.time(a1$h2 <- (a1$h1 == "H") * 1)
>   #  user  system elapsed
>   #  0.37    0.17    0.56
>   a12 <- a1
>   all.equal(a11,a12)
>   #[1] TRUE
>
> Peter Ehlers
>

I got the same result. Petr's solution is the fastest. Good to know it.

Pascal Oettli

>> Regards,
>> Jin
>>
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