Convert numeric vector to binary (0/1) based on limit

You don't need to make newvector beforehand and using it as an argument to ifelse is causing the error.

Try this...

newvector <- ifelse( p>=0.5 , 1 , 0 )

But even better just do it vectorised...

newvector <- as.integer( p >= 0.5 )

Just use :

newvector <- ifelse(p>=0.5,1,0)

The second and third arguments of ifelse are not expressions but the values to be returned.

You could also use findInterval for this particular case:

findInterval(p, .5)