I am a little confused about the switch statement in R. Simply googling the function I get an example as follows:
A common use of switch is to branch according to the character value of one of the arguments to a function.
> centre <- function(x, type) {
+ switch(type,
+ mean = mean(x),
+ median = median(x),
+ trimmed = mean(x, trim = .1))
+ }
> x <- rcauchy(10)
> centre(x, "mean")
[1] 0.8760325
> centre(x, "median")
[1] 0.5360891
> centre(x, "trimmed")
[1] 0.6086504
However this just seems to be the same as just having a bunch of if statements designated for each type
Is that all there is to switch()? Can someone give me further examples and better applications?
Answer
Well, timing to the rescue again. It seems switch is generally faster than if statements.
So that, and the fact that the code is shorter/neater with a switch statement leans in favor of switch:
# Simplified to only measure the overhead of switch vs if
test1 <- function(type) {
switch(type,
mean = 1,
median = 2,
trimmed = 3)
}
test2 <- function(type) {
if (type == "mean") 1
else if (type == "median") 2
else if (type == "trimmed") 3
}
system.time( for(i in 1:1e6) test1('mean') ) # 0.89 secs
system.time( for(i in 1:1e6) test2('mean') ) # 1.13 secs
system.time( for(i in 1:1e6) test1('trimmed') ) # 0.89 secs
system.time( for(i in 1:1e6) test2('trimmed') ) # 2.28 secs
Update With Joshua's comment in mind, I tried other ways to benchmark. The microbenchmark seems the best. ...and it shows similar timings:
> library(microbenchmark)
> microbenchmark(test1('mean'), test2('mean'), times=1e6)
Unit: nanoseconds
expr min lq median uq max
1 test1("mean") 709 771 864 951 16122411
2 test2("mean") 1007 1073 1147 1223 8012202
> microbenchmark(test1('trimmed'), test2('trimmed'), times=1e6)
Unit: nanoseconds
expr min lq median uq max
1 test1("trimmed") 733 792 843 944 60440833
2 test2("trimmed") 2022 2133 2203 2309 60814430
Final Update Here's showing how versatile switch is:
switch(type, case1=1, case2=, case3=2.5, 99)
This maps case2 and case3 to 2.5 and the (unnamed) default to 99. For more information, try ?switch