Switch Statements in R (Unpacking Arguments)

Question

Google search doesn't return much on this. How do you unpack arguments in R?

For instance if I try to use switch in R like

switch("AA",c("AA"=5,"BB"=6))

I will get back c("AA"=5,"BB"=6) when in reality, I want 5.

Essentially, I want to be able to do switch("AA","AA"=5,"BB"=6) with a vector mapping.

@user1431282 What do you mean by unpacking arguments. Does this in the python sense ? — agstudy, Mar 25 '13 at 23:13
@agstudy I think he thinks about this http://stackoverflow.com/questions/3414078/unpacking-argument-lists-for-ellipsis-in-r?rq=1 — Qbik, Mar 25 '13 at 23:17
@Qbik thanks. It is the Python sense of the term.( as it is confirmed in the link). — agstudy, Mar 25 '13 at 23:19

score 3 · Accepted Answer · answered Mar 25 '13 at 23:16

3

This is a bit of a workaround, but try:

do.call("switch", append(list("AA"), list("AA"=5, "BB"=6)))

The do.call() allows you to pass a list of arguments into switch().

answered Mar 25 '13 at 23:16

+1 - or `do.call(switch, as.list(c(EXPR = "AA", c("AA"= 5,"BB"= 6))))` – flodel Mar 26 '13 at 00:54
Couldn't this be simplified to `do.call("switch", append("AA", list("AA"=5, "BB"=6)))`. What does the `list("AA")` do? – Thomas May 08 '13 at 20:08
@Thomas It can be shortened as you suggest. The `list("AA")` was to insure that there wasn't any type coercion to go wrong. Your shortened version is converting a one element character vector to a one element list before appending the other list. – May 08 '13 at 20:25

IRTFM · Answer 2 · 2016-01-04T21:32:14.883

3

This is how switch was intended to be used. The first argument gets evaluated and match to the first elements of the succeeding pairlists:

 aa <- "AA"
 switch(aa,"AA"=5,"BB"=6)
#[1] 5
 switch("BB","AA"=5,"BB"=6)
#[1] 6

At least that is the strategy for 'character' arguments. The process for numeric arguments is different. One needs to read the Details section of ?switch carefully.

edited Jan 04 '16 at 21:32

answered Mar 25 '13 at 23:45

IRTFM

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score 2 · Answer 3 · answered Mar 25 '13 at 23:15

2

Your example is rather short, mayby you could obtain demanded functionality this way :

my.vector = c("AA"=5,"BB"=6)
my.vector[names(my.vector ) == "AA"]

AA 
 5

?

answered Mar 25 '13 at 23:15

Qbik

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score 2 · Answer 4 · answered Mar 26 '13 at 00:13

2

> c("AA"=5,"BB"=6)["AA"]
AA 
 5 
> c("AA"=5,"BB"=6)["BB"]
BB 
 6

answered Mar 26 '13 at 00:13

Julián Urbano

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Switch Statements in R (Unpacking Arguments)

4 Answers4