[R] Why does R do this?

[Thierry Onkelinx]

Dear Nick,

The best solution is not to use which() but directy use the logical test.
This will work in case the condition is always FALSE and which() returns a
integer(0). And it is much faster too.
z <- y > 3
y[!z]

library(microbenchmark)
microbenchmark(
  y[!y > 3],
  y[-which(y > 3)]
)

Best regards,




ir. Thierry Onkelinx
Statisticus / Statistician

Vlaamse Overheid / Government of Flanders
INSTITUUT VOOR NATUUR- EN BOSONDERZOEK / RESEARCH INSTITUTE FOR NATURE AND
FOREST
Team Biometrie & Kwaliteitszorg / Team Biometrics & Quality Assurance
thierry.onkelinx using inbo.be
Havenlaan 88 bus 73, 1000 Brussel
www.inbo.be

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Op di 8 jan. 2019 om 10:29 schreef Nick Wray via R-help <
r-help using r-project.org>:

> y<-c(1,2,3)
> z<-which(y>3)
> z
> y<-y[-z]
> y
>
> In the work I'm doing I often have this situation and have to make sure
> that I condition on z being non-zero as y is now numeric(0) rather than the
> set c(1,2,3).  Why does R do this?  Wouldn't it be more sensible for R to
> simply leave the host set unchanged if there are no elements to take out?
>
> Any thoughts?
>
> Thanks, Nick Wray
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>
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