Convert binary vector to decimal

Question

I have a vector of a binary string:

a<-c(0,0,0,1,0,1)

I would like to convert this vector into decimal.

I tried using the compositions package and the unbinary() function, however, this solution and also most others that I have found on this site require g-adic string as input argument.

My question is how can I convert a vector rather than a string to decimal?

to illustrate the problem:

library(compositions)
unbinary("000101") 
[1] 5

This gives the correct solution, but:

unbinary(a)
unbinary("a")
unbinary(toString(a)) 

produces NA.

Answer 1

You could try this function

bitsToInt<-function(x) {
    packBits(rev(c(rep(FALSE, 32-length(x)%%32), as.logical(x))), "integer")
}

a <- c(0,0,0,1,0,1)
bitsToInt(a)
# [1] 5

here we skip the character conversion. This only uses base functions.

It is likely that

 unbinary(paste(a, collapse=""))

would have worked should you still want to use that function.

Answer 2

There is a one-liner solution:

Reduce(function(x,y) x*2+y, a)

Explanation:

Expanding the application of Reduce results in something like:

Reduce(function(x,y) x*2+y, c(0,1,0,1,0)) = (((0*2 + 1)*2 + 0)*2 + 1)*2 + 0 = 10

With each new bit coming next, we double the so far accumulated value and add afterwards the next bit to it.

Please also see the description of Reduce() function.

Answer 3

If you'd like to stick to using compositions, just convert your vector to a string:

library(compositions)
a <- c(0,0,0,1,0,1)
achar <- paste(a,collapse="")
unbinary(achar)
[1] 5

Answer 4

This function will do the trick.

bintodec <- function(y) {
  # find the decimal number corresponding to binary sequence 'y'
  if (! (all(y %in% c(0,1)))) stop("not a binary sequence")
  res <- sum(y*2^((length(y):1) - 1))
  return(res)
}