Function to find the start and end of conditional selection - r

Question

I have a data that looks as follows:
Date | Time | Temperature
16995 | "12:00" | 23
16995 | "12:30" | 24
...
17499 | "23:30" | 23
17500 | "00:00" | 24
I'm writing a function to select a range of cases based on certain start and end time points. To do this I need to determine the start_pt and end_pt indices which should match with a pair of rows in the dataframe.
select_case <- function(df,date,time) {
start_pt = 0
end_pt = 0
for (i in 1:nrow(df)) {
if ((date[i] == 17000) & (time[i] == "12:00")) {
start_pt <- i
return(start_pt)
} else {
next
}
}
for (i in start_pt:nrow(df)) {
if (date[i] == 17500) {
end_pt <- i - 1
return(end_pt)
break
} else {
next
}
}
return(df[start_pt:end_pt,])
}
When I called:
test <- select_case(data,data$Date,data$Time)
test
I expect the following:
Date | Time | Temperature
17000 | "12:00" | 23
17000 | "12:30" | 24
...
17499 | "23:00" | 23
17499 | "23:30" | 23
Instead i got
[1] 1
Not sure where i got it wrong here. When I separately ran each of the two for-loops from R console and substituting in the corresponding arguments for each loop, i got the correct indices for both start_pt and end_pt.

Answer 1

I tried putting each loop in a separate function, named sta(date,time) and end(date). Then I bind them in the following function:
binder <- function(date,time) {
return(sta(date,time),end(date))
}
and call
sta_end <- binder(date,time)
I got the error:
Error in return(sta(date, time), end(date)) :
multi-argument returns are not permitted
So i combined them and it worked:
binder <- function(date,time) {
return(c(sta(date,time),end(date)))
}
sta_end <- binder(date,time)
[1] 1 <an index for end_pt>
So the mistake i made in my original function is that i use return() 3 times and the function will only return the first one which is start_pt. So I took out the first two return() and retained the last one:
return(df[start_pt:end_pt,])
This worked, i got the expected result.