[R] flip certain bits in vector

[David Winsemius]

I do not think your wetware processed the inputs correctly. The second  
bit should not have been flipped:

Try this loop free index based solution:

  b <- c( 1, 0, 1, 0, 1, 0, 1, 0, 1, 0)
  r <- b
  r[p] <- 0 + !r[p]  # adding 0 converts logical TRUE/FALSE  to 0/1
  r
  [1] 0 0 0 0 0 0 0 0 1 0

The "if" statement is for control but you might have succeeded with an  
ifelse function which is generally more useful for conditional  
modification of vectors. It could have been used if the transformation  
were not binary.

-- 
David Winsemius

On Apr 19, 2009, at 3:24 PM, Esmail wrote:

> I have a string of binary values, and I would like to flip certain
> bits in a set of positions.
>
> Let's say the
>
> vector p contains position [1, 3, 5, 7]
> vector b contains bits   [1, 0, 1, 0, 1, 0, 1, 0, 1, 0]
> result r should be       [0, 1, 0, 0, 0, 0, 0, 0, 1, 0]
>
> in pseudo code this would be something like
>
> ---
>
> r = c()
>
> for (i in 1:10)
>  if (i in p)
>     r = c(r, flip[i])
>
> r
> ----
>
> doesn't work :-)  R doesn't like the if statement.
>
> Is there a nice, concise way to do this? The vector contents and
> size will vary, but length of p <= b.
>
> Thanks,
> Esmail