R help - Apr 2009 - flip certain bits in vector

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

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

try this:
> b <- c(1, 0, 1, 0, 1, 0, 1, 0, 1, 0)
> p <- c(1, 3, 5, 7)
> b[p] <- ifelse(b[p] == 0, 1, 0)
> b
 [1] 0 0 0 0 0 0 0 0 1 0


On Sun, Apr 19, 2009 at 3:24 PM, Esmail <esmail.js at gmail.com>
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
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

David Winsemius wrote:
> I do not think your wetware processed the inputs correctly. The second 
> bit should not have been flipped:
Ooops .. yes you are right!
> 
> 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
Great! .. thanks ... I appreciate the hlep,


Esmail