R help - Nov 2003 - Increment element of vector and efficiency

Hi all,

Thanks for the incredibly quick help with the "%in%"...

There's a second question, though: I'd like to increment an element of a
vector if a certain event occurs, e.g.

    count[event] <- count[event] + 1;         # works, but...

Is this efficient? I wonder whether R needs to subset the count vector 
on both sides of the assignment operator (i.e., twice), or whether 
there's a shortcut like "++" in C, e.g. "count[i]++" or
similar?

Pascal

I think that's about as efficient as you can get.  I'm not sure of the 
underlying details.  There was some discussion recently of having the 
equivalent of a "+=" operator but currently R has no such thing.

-roger

Pascal A. Niklaus wrote:
> Hi all,
> 
> Thanks for the incredibly quick help with the "%in%"...
> 
> There's a second question, though: I'd like to increment an element
of a
> vector if a certain event occurs, e.g.
> 
>    count[event] <- count[event] + 1;         # works, but...
> 
> Is this efficient? I wonder whether R needs to subset the count vector 
> on both sides of the assignment operator (i.e., twice), or whether 
> there's a shortcut like "++" in C, e.g.
"count[i]++" or similar?
> 
> Pascal
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>

On Thu, 2003-11-20 at 07:43, Pascal A. Niklaus wrote:
> Hi all,
> 
> Thanks for the incredibly quick help with the "%in%"...
> 
> There's a second question, though: I'd like to increment an element
of a
> vector if a certain event occurs, e.g.
> 
>     count[event] <- count[event] + 1;         # works, but...
> 
> Is this efficient? I wonder whether R needs to subset the count vector 
> on both sides of the assignment operator (i.e., twice), or whether 
> there's a shortcut like "++" in C, e.g.
"count[i]++" or similar?
> 
> Pascal

There is no increment operator in R. However, it would not be difficult
to create a function to increment a value:

increment <- function(x)
{
  eval.parent(substitute(x <- x + 1))
}
> x <- c(2, 5, 3, 8)
> increment(x[3])
> x
[1] 2 5 4 8
> increment(x[3])
> x
[1] 2 5 5 8
> increment(x[3])
> x
[1] 2 5 6 8
>From a practical standpoint however, it does not save any time of
course:
> system.time(increment(x[3]))
[1] 0 0 0 0 0
> system.time(x[3] <- x[3] + 1)
[1] 0 0 0 0 0


HTH,

Marc Schwartz