What is the 'idiomatic' way of writing a vectorized switch statement?
That is, I would like to write, e.g.,
vswitch( c('a','x','b','a'),
a= 1:4,
b=11:14,
100 )
=> c(1, 100, 13, 4 )
equivalent to
ifelse( c('a','x','b','a') == 'a', 1:4,
ifelse( c('a','x','b','a') == 'b', 11:14,
100 ) )
A simple way of doing this is (leaving aside the default case):
colchoose <- function(frame,selector)
mapply(function(a,b)frame[a,b],seq_along(frame[1]),selector))
colchoose( data.frame(a=1:4,b=11:14), c('a','b','b','a'))
=> c(1,11,11,1)
But of course this is not very efficient compared to the way ifelse works.
Is there a standard function or idiom for this (am I missing something
obvious?), or should I write my own?
-s
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