R Storing Values from For Loop to Data Frame - r

Question

I am trying to write a function that has 2 arguments: column name and ranking number. The function will read a CSV file that has hospitals from every state. The function should return a data frame with the hospital name that was at the specified rank.
My solution has been to split the main CSV file by state, order each data frame by the desired column, loop through each state's data frame, grab the row (where row number = rank number), store each state's hospital name into a vector, then create a dataframe using the vector from the loop.
When I test each part of my function in the console, I am able to receive the results I need. However, when I run the function altogether, it isn't storing the hospital names as desired.
Here's what I have:
rankall <- function(outcome, num = "best") {
outcomedf <- read.csv("outcome-of-care-measures.csv")
#using this as a test
outcomedf <- outcomedf[order(outcomedf[, 11], outcomedf[, 2]), ]
#create empty vectors for hospital name and state
hospital <- c()
state <- c()
#split the read dataframe
splitdf <- split(outcomedf, outcomedf$State)
#for loop through each split df
for (i in 1:length(splitdf)) {
#store the ranked hospital name into hospital vector
hospital[i] <- as.character(splitdf[[i]][num, 2])
#store the ranked hospital state into state vector
state[i] <- as.character(splitdf[[i]][, 7])
}
#create a df with hospital and state
rankdf <- data.frame(hospital, state)
return(rankdf)
}
When I run the function altogether, I receive NA in my 'hospital' column, but when I run each part of the function individually, I am able to receive the desired hospital names. I'm a little confused as to why I am able to run each individual part of this function outside of the function and it returns the results I want, but not when I run the function as a whole. Thank you.

Answer 1

This question is related to Programming Assignment 3 in the Johns Hopkins University R Programming course on Coursera. As such, we can't provide a "corrected version" of the code because doing so would violate the Coursera Honor code.
When run with the default settings, your implementation of the rankall() function fails because when you use num in the extract operator there is no ["best",2] row. If you run your code as head(rankall("heart attack",1)) it produces the following output.
> head(rankall("heart attack",1))
hospital state
1 PROVIDENCE ALASKA MEDICAL CENTER AK
2 CRESTWOOD MEDICAL CENTER AL
3 ARKANSAS HEART HOSPITAL AR
4 MAYO CLINIC HOSPITAL AZ
5 GLENDALE ADVENTIST MEDICAL CENTER CA
6 ST MARYS HOSPITAL AND MEDICAL CENTER CO
To completely correct your function, you'll need to make the following changes.
Add code to sort the data by the desired outcome column: heart attack, heart failure, or pneumonia
Add code to handle the condition when a state does not have enough hospitals to return a valid result (i.e. the 43rd ranked hospital for pneumonia in Puerto Rico
Add code to handle "best" and "worst" as inputs to the num argument