[R] Finding indices with a certain property

Göran Broström gb at stat.umu.se
Tue Dec 7 19:07:58 CET 1999

```Quick answers to my question:

which(x < 0)

but also

> indices<-function(x)seq(along=x)[x]
> x <- c(1, -1, 3, 3, -2)
> indices(x<0)
[1] 2 5

from some.

The last one is essentially the definition of  which, I think.
I had completely forgotten  which  (where?!?)

Thanks to Thomas Lumley, Jonathan Rougier, Martin Maechler,
Peter Dalgaard, Brian Ripley!

Göran

Original question:

> > I want the indices  i  for which  x[i] < 0 (say):
> >
> > > x <- c(1, -1, 3, 3, -2)
> > > where.negative(x)
> > [1] 2 5
> >
> > Surely  where.negative  is something simple, but how?

--------------------------------------------------------------
Göran Broström
Department of Statistics              tel: +46 90 786-5223
Umeå University                       fax: +46 90 786-6614
S-90187 Umeå, Sweden               e-mail:  gb at stat.umu.se

http://www.stat.umu.se/~gb          ftp://capa.stat.umu.se
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