Question

I was trying to learn R using a book. I was trying to do an example where for each row of the matrix, the corresponding element of the vector will be either 1 or 0, depending on whether the majority of the
first d elements in that row is 1 or 0. The code used was:-

copymaj <- function(rw,d) {
   maj <- sum(rw[1:d]) / d
   return(if(maj > 0.5) 1 else 0)
}

 x
    [,1] [,2] [,3] [,4] [,5]
[1,]  1    0    1    1    0
[2,]  1    1    1    1    0
[3,]  1    0    0    1    1
[4,]  0    1    1    1    0

apply(x,1,copymaj,3)

It is showing the above error. Also if I do apply(x,1,copymaj(3)), still error is shown.

R 2.13 is installed
Please help!

Answer 1

As @BenBarnes pointed out, you probably misspelled sum, I think you wrote sim instead of sum.

I was able to reproduce your error by doing:

copymaj0 <- function(rw,d) {
  maj <- sim(rw[1:d]) / d    # here you have sim, this causes the error 
  return(if(maj > 0.5) 1 else 0)
}

copymaj1 <- function(rw,d) {
  maj <- sum(rw[1:d]) / d    # here you have sum which works well for me 
  return(if(maj > 0.5) 1 else 0)
}

x <- matrix(c(1,0,1,1,0,
         1,1,1,1,0,
         1,0,0,1,1,
         0,1,1,1,0), ncol=5, byrow=TRUE)

apply(x,1,copymaj0,3) # prints error
Error in FUN(newX[, i], ...) : could not find function "sim"

apply(x,1,copymaj1,3) # works well
[1] 1 1 0 1

I really think you misspelled sum.

apply(x,1,copymaj1(3)) won’t work becase if you read ?apply you’ll see
apply(X, MARGIN, FUN, ...), then apply(x,1,copymaj1(3)) wil produce an error because
... replaces the arguments to FUN (d=3 in your case) is missed. In order to pass optional arguments to your fun you have to use ... as in apply(x,1,copymaj1,3) but not using apply(x,1,copymaj1(3)).