R help - May 2009 - Replace is leaking?

Okay, someone explain this behaviour to me:

Browse[1]> replace(rep(0, 4000), temp1[12] , temp2[12])[3925]
[1] 0.4462404
Browse[1]> temp1[12]
[1] 3926
Browse[1]> temp2[12]
[1] 0.4462404
Browse[1]> replace(rep(0, 4000), 3926 , temp2[12])[3925]
[1] 0

For some reason, R seems to shift indices along when doing this replacement.

Has anyone encountered this bug before? It seems to crop up from time
to time, seemingly at random. Any idea for a fix? Reassigning the
variables seems to preserve the magicness of the numbers. It all seems
very bizarre and worrying.

If anyone is interested in a R workspace to reproduce this, email me.
This is running in R 2.9.

Zhou Fang

Oh hang on, I've figured it out.

Rounding error, doh. Somewhere along the line I got lazy and took the 
weighted average of two values that are equal. as.integer truncates, so, 
yeah. Never mind.

Zhou Fang

On 28/05/2009, at 12:36 PM, Zhou Fang wrote:
> Okay, someone explain this behaviour to me:
>
> Browse[1]> replace(rep(0, 4000), temp1[12] , temp2[12])[3925]
> [1] 0.4462404
> Browse[1]> temp1[12]
> [1] 3926
> Browse[1]> temp2[12]
> [1] 0.4462404
> Browse[1]> replace(rep(0, 4000), 3926 , temp2[12])[3925]
> [1] 0
>
> For some reason, R seems to shift indices along when doing this  
> replacement.
>
> Has anyone encountered this bug before? It seems to crop up from time
> to time, seemingly at random. Any idea for a fix? Reassigning the
> variables seems to preserve the magicness of the numbers. It all seems
> very bizarre and worrying.
>
> If anyone is interested in a R workspace to reproduce this, email me.
> This is running in R 2.9.
Doesn't happen to me:

  > temp1 <- sample(1:10000,20)
  > temp2 <- runif(20)
  > temp1[12] <- 3926
  > temp2[12] <- 0.4462404
  > temp1[12]
[1] 3926
  > temp2[12]
[1] 0.4462404
  > xxx <- replace(rep(0, 4000), temp1[12] , temp2[12])
  > xxx[3925]
[1] 0
  > xxx[3926]
[1] 0.4462404


OMMMMMMMMMMMMMMMMMM!

	cheers,

		Rolf Turner

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