# Scratching that itch from ifelse

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Okay, as I wrote yesterday, ifelse is rather slow, at least compared to working in C++. As my current project is using ifelse rather a lot, i decided to write a small utility function. In the expectation that I will collect a number of similar functions, I made a package out of it and posted it on github: https://github.com/ojessen/ojUtils

I get a speedup of about 30 times, independent of the target type.

Feedback and corrections greatly appreciated.

Thanks to the people at Travis for providing a free CI server which works directly with github. This of course is a tiny example, but it is good to know that the workflow to set this up can be done in 5 minutes.

And thanks to Romain Fraoncois for showing some Rcpp sugar:

.@ojessen I sent you a pull request leveraging Rcpp’s ifelse. Although maybe wait: Rcpp’s ifelse is broken … https://t.co/38P0mQc3aZ

— Romain Francois (@romain_francois) 20. Juni 2014

Some data:

# ifelseR.R

*post_000*

*Fri Jun 20 17:12:25 2014*

require(ojUtils) ## Loading required package: ojUtils require(microbenchmark) ## Loading required package: microbenchmark test = sample(c(T,F), size = 1e5, T) yes = runif(1e5) no = runif(1e5) microbenchmark(ifelse(test, yes, no), ifelseC(test, yes, no)) ## Loading required package: Rcpp ## Unit: microseconds ## expr min lq median uq max neval ## ifelse(test, yes, no) 31925 33404.8 34065.1 58083.5 71891 100 ## ifelseC(test, yes, no) 620 647.5 721.8 817.7 209254 100 test = sample(c(T,F), size = 1e5, T) yes = rep("a", 1e5) no = rep("b", 1e5) microbenchmark(ifelse(test, yes, no), ifelseC(test, yes, no)) ## Unit: milliseconds ## expr min lq median uq max neval ## ifelse(test, yes, no) 57.313 58.763 59.626 72.435 87.92 100 ## ifelseC(test, yes, no) 1.747 1.837 1.926 2.749 29.56 100 test = sample(c(T,F), size = 1e5, T) yes = rep(1L, 1e5) no = rep(2L, 1e5) microbenchmark(ifelse(test, yes, no), ifelseC(test, yes, no)) ## Unit: microseconds ## expr min lq median uq max neval ## ifelse(test, yes, no) 30747.6 31868.5 32274.8 32829.0 59412 100 ## ifelseC(test, yes, no) 453.7 548.9 581.5 646.2 27575 100 test = sample(c(T,F), size = 1e5, T) yes = rep(T, 1e5) no = rep(F, 1e5) microbenchmark(ifelse(test, yes, no), ifelseC(test, yes, no)) ## Unit: microseconds ## expr min lq median uq max neval ## ifelse(test, yes, no) 29331.2 31167.3 31719.7 32455.3 60589 100 ## ifelseC(test, yes, no) 460.1 537.1 566.8 640.7 27118 100

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