The switch() function in R tests an expression against elements
of a list. If the value evaluated from the
expression matches item from the list, the corresponding value is returned.
Syntax of switch() function
switch (expression, list)
Here, the expression is evaluated and based on this value, the corresponding item in the list is returned.
If the value evaluated from the expression matches with more than
one item of the list, switch() function returns the first matched
item.
Example: switch() function
If the value evaluated is a number, that item of the list is returned.
> switch(2,"red","green","blue")
[1] "green"
> switch(1,"red","green","blue")
[1] "red"
In the above example, "red","green","blue" form a three item
list.
The switch() function returns the corresponding item to the
numeric value evaluated.
If the numeric value is out of range (greater than the number of items in the
list or smaller than 1), then, NULL is returned.
> x <- switch(4,"red","green","blue")
> x
NULL
> x <- switch(0,"red","green","blue")
> x
NULL
Example: switch() Function with as String Expression
The expression used in the switch () function can be a
string as well. In this case, the matching named item's value is returned.
> switch("color", "color" = "red", "shape" = "square", "length" = 5)
[1] "red"
Here, "color" is a string which matches with the first item of
the list. Hence, we are getting "red" as an output.
> switch("length", "color" = "red", "shape" = "square", "length" = 5)
[1] 5
Similarly, "length" expression matches with the last item of the
list. Hence, we are getting 5 as an output.
Also check this example to make a simple calculator in R using switch() function.