Select One of a List of Alternatives

Usage

switch(EXPR, ...)

Arguments

EXPR an expression evaluating to a number or a character string.
... the list of alternatives, given explicitly.

Description

switch evaluates EXPR. If the value is an integer between 1 and nargs()-1 then the corresponding element of ... is evaluated and the result returned.

If EXPR returns a character string then that string is used to match the names of the elements in .... If there is an exact match then that element is evaluated and the result returned. In the case of no match, if there's a further argument in switch(..) that one is returned, otherwise NULL.

Examples

centre <- function(x, type) {
  switch(type,
	mean = mean(x),
        median = median(x),
        trimmed = mean(x, trim = .1))
}
x <- rcauchy(10)
centre(x, "mean")
centre(x, "median")
centre(x, "trimmed")

ccc <- c("b","QQ","a","A","b")
for(ch in ccc) cat(ch,":",switch(ch, a=1, b=2:3),		"\n")
for(ch in ccc) cat(ch,":",switch(ch, a=1, b=2:3, "Otherwise: last arg."),"\n")

## Numeric EXPR don't allow an `otherwise':
for(i in c(-1:3,9))  print(switch(i, 1,2,3,4))


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