switch {base} | R Documentation |
switch
evaluates EXPR
and accordingly chooses one of the
further arguments (in ...
).
switch(EXPR, ...)
EXPR |
an expression evaluating to a number or a character string. |
... |
the list of alternatives, given explicitly. |
If the value of EXPR
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 returned if there is one,
otherwise the next element is chosen, e.g.,
switch("cc", a=1, cc=, d=2)
evaluates to 2
.
In the case of no match, if there's a further argument in switch
that one is returned, otherwise NULL
.
Beware of partial matching: an alternative E = foo
will match
the first argument EXPR
unless that is named. See the examples
for good practice in naming the first argument.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
require(stats) 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","bb") for(ch in ccc) cat(ch,":",switch(EXPR = ch, a=1, b=2:3), "\n") for(ch in ccc) cat(ch,":",switch(EXPR = ch, a=, A=1, b=2:3, "Otherwise: last"),"\n") ## Numeric EXPR don't allow an 'otherwise': for(i in c(-1:3,9)) print(switch(i, 1,2,3,4))