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

[Peter Ehlers]

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

> Regards,
> Jin
>
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