[R] Odd behaviour of removing 'nothing' from an array or data frame

[hadley wickham]

> As Peter said, it's the value that counts, not the way you calculated
> it.  If you print -c(2,3,5) you get three negative numbers.  If you
> print -integer(0), you don't get any.  The first case is asking for
> elements to be left out, the second isn't.
>
> The moral of the story is to use logical indices rather than negative ones:
>
> dubious.records <- peoples.heights$heights > 2.5
> peoples.heights = peoples.heights[!dubious.records,]

Unfortunately, there are some "matching" functions that return numeric
indices, not logical vectors (eg. grep).  For this case I created an
"unwhich" function - but is there a better way to proceed?

Hadley