HW assignment for learning R from scratch - r

Question

So I am taking a course that requires learning R and I am struggling with one of the questions:
In this question, you will practice calling one function from within another function. We will estimate the probability of rolling two sixes by simulating dice throws. (The correct probability to four decimal places is 0.0278, or 1 in 36).
(1) Create a function roll.dice() that takes a number ndice and returns the result of rolling ndice number of dice. These are six-sided dice that can return numbers between 1 and 6. For example roll.dice(ndice=2) might return 4 6. Use the sample() function, paying attention to the replace option.
(2) Now create a function prob.sixes() with parameter nsamples, that first sets j equal to 0, and then calls roll.dice() multiple times (nsample number of times). Every time that roll.dice() returns two sixes, add one to j. Then return the probability of throwing two sixes, which is j divided by nsamples.
I am fine with part one, or at least I think so, so this is what I have
roll.dice<-function(ndice)
{
roll<-sample(1:6,ndice,TRUE)
return(roll)
}
roll.dice(ndice=2)
but I am struggling with part two. This is what I have so far:
prob.sixes<-function(nsamples) {
j<-vector
j<-0
roll.dice(nsamples)
if (roll.dice==6) {
j<-j+1
return(j)
}
}
prob.sixes(nsamples=3)
Sorry for all the text, but can anybody help me?

Answer 1

Your code has a couple of problems that I can see. The first one is the interpretation of the question. The question says:
Now create a function prob.sixes() with parameter nsamples, that first sets j equal to 0, and then calls roll.dice() multiple times (nsample number of times).
Check on your code, are you doing this? Or are you calling roll.dice() a single time? Look for ways to do the same thing (in your case, roll.dice) several times; you may consider the function for. Also, here, you need to store the result of this function on a variable, something like
rolled = roll.dice(2)
Second problem:
Every time that roll.dice() returns two sixes, add one to j.
You are checking if roll.dice==6. But this has two problems. First, roll.dice is a function, not a variable. So it will never be equal to 6. Also, you don't want to check if this variable is equal to six. You should ask whether this variable is equal to a pair of sixes. How can you write "a pair of sixes"?