R help - Sep 2012 - effective way to return only the first argument of "which()"

Hi,

I was looking for a function like "which()" but only returns the first
argument.
Compare:

x <- c(1,2,3,4,5,6)
y <- 4
which(x>y)

returns:
5,6

which(x>y)[1]
returns:
5

which(x>y)[1] is exactly what i need. I did use this but the dataset
is too big (~18 mio. Points).
That's why i need a more effective way to get the first element of a
vector which is bigger/smaller than a specific number.

I found "match()" but this function only works for equal numbers.



Thanks,
Nico

On Wed, Sep 19, 2012 at 3:20 PM, Mike Spam <ichmagspam at googlemail.com>
wrote:
> Hi,
>
> I was looking for a function like "which()" but only returns the
first argument.
> Compare:
>
> x <- c(1,2,3,4,5,6)
> y <- 4
> which(x>y)
>
> returns:
> 5,6
>
> which(x>y)[1]
> returns:
> 5
>
> which(x>y)[1] is exactly what i need. I did use this but the dataset
> is too big (~18 mio. Points).
> That's why i need a more effective way to get the first element of a
> vector which is bigger/smaller than a specific number.
>
> I found "match()" but this function only works for equal numbers.
>
It's long felt a little hack-ish but you can actually use which.min()
or which.max() on logical vectors for just this purpose.

x <- sample(20)

which.max(x < 5) # first x satisfying the condition.

Cheers,
Michael
>
>
> Thanks,
> Nico
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

?which.max
---------------------------------------------------------------------------
Jeff Newmiller                        The     .....       .....  Go Live...
DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live
Go...
                                      Live:   OO#.. Dead: OO#..  Playing
Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
/Software/Embedded Controllers)               .OO#.       .OO#.  rocks...1k
--------------------------------------------------------------------------- 
Sent from my phone. Please excuse my brevity.

Mike Spam <ichmagspam at googlemail.com> wrote:
>Hi,
>
>I was looking for a function like "which()" but only returns the
first
>argument.
>Compare:
>
>x <- c(1,2,3,4,5,6)
>y <- 4
>which(x>y)
>
>returns:
>5,6
>
>which(x>y)[1]
>returns:
>5
>
>which(x>y)[1] is exactly what i need. I did use this but the dataset
>is too big (~18 mio. Points).
>That's why i need a more effective way to get the first element of a
>vector which is bigger/smaller than a specific number.
>
>I found "match()" but this function only works for equal numbers.
>
>
>
>Thanks,
>Nico
>
>______________________________________________
>R-help at r-project.org mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.

Hi,

Thanks Michael, but i think this is even slower.

 x <-sample(20000000)
 which(x < 5)[1]
 which.max(x < 5)
 system.time(for(i in 1:100) which.max(x < 5))
       User      System verstrichen
      60.84       13.70       86.33
 system.time(for(i in 1:100) which(x < 5)[1])
       User      System verstrichen
      40.45        8.25       48.95



Thanks,
Nico