R - Print values using for, while, and repeat loop - r

Question

I am having trouble again with my code. Here is the question and what I have right now:
# 2. Draw a random sample of size n=20 from a uniform distribution in 0 and 1 using
# runif(20). Sequentially, print values using the following rules:
# i. Print a value if it is less than 0.3 or more than 0.8, but skip it
# (don’t print the value) if it is in (0.1, 0.2],
# ii. Skip the entire process if you find a value in [0.4,0.5].
# Write three separate R codes using (a) for loop, (b) while loop
# and (c) repeat loop.
# (a) for loop
n = runif(20)
for (val in n){
if (val > 0.1 & val <= 0.2){
next
} else if (val < 0.3 | val > 0.8){
print(val)
} else if (val >= 0.4 & val <= 0.5){
print(val)
break
}
}
# (b) while loop
n = 1
m = runif(20)
while(n < 20){
if (m > 0.1 & m <= 0.2){
next
} else if (m < 0.3 | m > 0.8){
print(m)
} else if (m >= 0.4 & m <= 0.5){
print(m)
break
}
n = n + 1
}
# (c) repeat loop
n = 1
m = runif(20)
repeat{
if (m > 0.1 & m <= 0.2){
next
} else if (m < 0.3 | m > 0.8){
print(val)
} else if (m >= 0.4 & m <= 0.5){
print(m)
break
}
}
Part (a) for loop is working perfectly.
My only issue is (b) while loop and (c) repeat loop. He didn't do a good job in class or notes going over a while loop and repeat loop. Please help.

Answer 1

The object m that you created has a length of 20, so when you go to test it with something like if (m > 0.1 & m <= 0.2), R only tests the first item in your object. To solve this, you'll need to index m with n, your loop counter. In other words, don't use m in your tests, but use m[n] instead. In all it should look like this:
n <- 1
m <- runif(20)
while(n < 20){
if (m[n] > 0.1 & m[n] <= 0.2){
next
} else if (m[n] < 0.3 | m[n] > 0.8){
print(m[n])
} else if (m[n] >= 0.4 & m[n] <= 0.5){
print(m[n])
break
}
n <- n + 1
}
You should be able to use a similar approach for part c. (Also note that in part c you have print(val) at one point.)
Hope that helps!

Answer 2

Apparently the exercise if for you to sort it out, but OK, I'll post a solution.
# (b) while loop
n = 1
m = runif(20)
while(n <= 20){
if (m[n] > 0.1 & m[n] <= 0.2){
n = n + 1
next
} else if (m[n] < 0.3 | m[n] > 0.8){
print(m[n])
} else if (m[n] >= 0.4 & m[n] <= 0.5){
print(m[n])
break
}
n = n + 1
}
# (c) repeat loop
n = 0
m = runif(20)
repeat{
if(n < 20)
n <- n + 1
else
break
if (m[n] > 0.1 & m[n] <= 0.2){
next
} else if (m[n] < 0.3 | m[n] > 0.8){
print(m[n])
} else if (m[n] >= 0.4 & m[n] <= 0.5){
print(m[n])
break
}
}
As a final note, whenever pseudo-random number generators are used you should set the initial value in order for the results to be reproducible. This is done like this:
set.seed(6019) # or any other value, 6019 is the seed
This is put before the first call to runif.