User defined function within for-loops - r

Question

I am working on a project in which I am simulating 8 classroom social networks over 6 weeks, so 30 iterations. Students will nominate each other based on a number of factors, and I plan to simulate a number of conditions in which I remove or add some of these factors to the simulation. In other words, I'm going to be repeating a lot of code, so I'd rather use functions rather than cutting and pasting where ever possible.
Right now, I'm trying to create a function that adjusts the probability of one student selecting another based on the similarity of their emotions. When I include it in a set of nested for for loops, this works just fine:
num_students <- 5
names_students <- letters[1:num_students]
student_emotion <- sample(round(runif(5, min = -5, max = 5), digits = 1))
student_emotion_df <- cbind.data.frame(names_students, student_emotion)
probs <- rep(1/num_students, 5)
row_prob <- vector(length = 5)
for(i in 1:num_students){
for(q in 1:num_students){
if(abs(student_emotion[i]-student_emotion[q]) >= 0 &
abs(student_emotion[i]-student_emotion[q]) <= .5){
row_prob[q] <- 1*probs[q]
} else if(abs(student_emotion[i]-student_emotion[q]) > .5 &
abs(student_emotion[i]-student_emotion[q]) <= 1) {
row_prob[q] <- .75 * probs[q]
}
else {
row_prob[q] <- .5 * probs[q]
}
}
}
The row_prob object is a vector of probabilities a student i, in the column, will select student q, in the rows.
I've created a user-defined function based on the same code, and that works:
emotion_difference_fun <- function(probs){
for(q in 1:num_students){
if(abs(student_emotion[i]-student_emotion[q]) >= 0 &
abs(student_emotion[i]-student_emotion[q]) <= .5){
row_prob[q] <- 1*probs[q]
} else if(abs(student_emotion[i]-student_emotion[q]) > .5 &
abs(student_emotion[i]-student_emotion[q]) <= 1) {
row_prob[q] <- .75 * probs[q]
}
else {
row_prob[q] <- .5 * probs[q]
}
}
return(row_prob)
}
emotion_difference_fun(probs)
But when I try to embed that function within the for loop iterating through the columns, row_prob returns as an empty vector:
for(i in 1:num_students){
emotion_difference_fun(probs)
}
Any thoughts on how I can get this to work?
Thanks for any help you're able to offer.

Answer 1

If I understood your question properly, then you need to assign the results in your last 'for' loop:
for(i in 1:num_students){
if(i == 1) out <- NULL
out <- c(out, emotion_difference_fun(probs))
}
out
Is that what you are looking for?
What I am unclear about though, is why in your second code section you are not looking for a 5*5 matrix. Eventually, when running that code, it doesn't matter that you did it for i = 5 students, because it will only save in row_prob your last iteration (student = 5).

Answer 2

You can use replicate to repeat the function emotion_difference_fun for num_students.
result <- replicate(num_students, emotion_difference_fun(probs))
You can also set simplify = FALSE to get output as list.
result <- replicate(num_students, emotion_difference_fun(probs),simplify = FALSE)