Question

Write an R function named fifth with a single vector argument x that calculates and returns the sample mean of he 5th, 10th, 15th, ... elements of x. You may assume that x has at least 5 elements.

Answer 1

The following code gives you the required functionality:

myFunction <- function(x)
{
   i <- 1
   j <- 1
   y <- vector()
  
   while(i<=length(x))
   {
       if( i %% 5 == 0)
       {
           y[j] <- x[i]
           j = j + 1
       }
       i = i + 1
   }
  res <- mean(y)
   return (res)
}

x <- c(1,2,3,4,5,6,7,8,9,3,5,45,6,43,3,3,43,23,23,43,23,23,32)
ans <- myFunction(x)
print(ans)

Output:

[1] 13.5

Code's link:

http://ideone.com/qZeVyX