How to order a column by group in R

Question

I have a data.frame (say "df") looks like following:

Hospital.Name | State | Mortality.Rate
'hospital_1'   | 'AA'  | 0.2
'hospital_2'   | 'AA'   | 0.3
'hospital_3'   | 'BB'  | 0.3
'hospital_4'   | 'CC'  | 0.5

(The Hospital.Name is unique)

Now I want to order the "Mortality.Rate" group by "State", i.e. order the rate within a certain state. If there is a tie in the rate, then "Hospital.Name" is used for resolve the tie.

The "order()" and "tapply()" functions came to my mind. I coded like this:

tapply(df$Mortality.Rate, df$State, order, df$Hospital.Name, na.last=NA)

However, an error "argument length differ" popped up. When "order" function is applied to a sliced "Rate", the second argument of order (i.e. df$Hospital.Name) is not sliced.

How could I pass the second argument (for resolution a tie in ordering) to tapply() or is there any other approaches?

Answer 1

If we already in loading needles (for this specific operation) packages, here's a package (data.table) that could be useful in a sense of sorting the data by reference (without copying it and the need of using <-) using the setorder or setkey functions

library(data.table)
setorder(setDT(df), State, Mortality.Rate, Hospital.Name)

Though, you could potentially mimic base R syntax and order the data while creating a copy (though with improved speed because data.table calls its forder under the hood)

setDT(df)[order(State, Mortality.Rate, Hospital.Name)]