R – switch() statement usage

rswitch-statement

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?

Best Solution

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

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