Subset by function's variable using $variable - r

Question

I am having trouble to subset from a list using a variable of my function.
rankhospital <- function(state,outcome,num = "best") {
#code here
e3<-dataframe(...,state.name,...)
if (num=="worst"){ return(worst(state,outcome))
}else if((num%in%b=="TRUE" & outcome=="heart attack")=="TRUE"){
sep<-split(e3,e3$state.name)
hosp.estado<-sep$state
hospital<-hosp.estado[num,1]
return(as.character(hospital))
I split my data frame by state (which is a variable of my function)
But hosp.estado<-sep$state doesn't work. I have also tried as.data.frame.
The function (rankhospital("NY"....) returns me a character(0).
When I feed the sep$state with sep$"NY" directly in code it works perfectly so I guess the problem is I can't use a function's variable to do this. Am I right? What could I use instead?
Thank you!!

Answer 1

If state is a variable in your function, you can refer to a column with the name given by state using: sep[state] or sep[[state]]. The first produces a data frame with one column named based on the value of state. The second produces an unnamed vector.
df=data.frame(NY=rnorm(10),CA=rnorm(10), IL=rnorm(10))
state="NY"
df[state]
# NY
# 1 -0.79533912
# 2 -0.05487747
# 3 0.25014132
# 4 0.61824329
# 5 -0.17262350
# 6 -2.22390027
# 7 -1.26361438
# 8 0.35872890
# 9 -0.01104548
# 10 -0.94064916
df[[state]]
# [1] -0.79533912 -0.05487747 0.25014132 0.61824329 -0.17262350 -2.22390027 -1.26361438 0.35872890 -0.01104548 -0.94064916
class(df[state])
# [1] "data.frame"
class(df[[state]])
# [1] "numeric"

Answer 2

It seems like you are trying to get the top hospital in a state. You don't want to split here (see the result of sep to see what I mean). Instead, use:
as.character(e3[e3$state.name==state, 1][num])
This hopefully does what you want.

Answer 3

You need sep[[state]] instead of sep$state to get the data frame out of your sep list, which matches the state parameter of your function. Like this:
e3 <- read.csv("https://raw.github.com/Hindol/data-analysis-coursera/master/HW3/hospital-data.csv")
state <- "WY"
num <- 1:5
sep<-split(e3,e3$State)
hosp.estado<-sep[[state]]
hospital<-hosp.estado[num,1]
as.character(hospital)
# [1] "530002" "530006" "530008" "530010" "530011"