The nested if…else statement is especially useful when you want to execute a certain block of code when a condition is met.
However, if you want to select values based only on a condition, you have a better option: Use the switch() function.
Syntax
Here’s the syntax of the switch() function:
switch() with String Expression
If the expression is a character string, switch() will return the value based on the name of the element.
# Select element by name and return its value
x <- "a"
v <- switch(x, "a"="apple", "b"="banana", "c"="cherry")
v
[1] "apple"
x <- "c"
v <- switch(x, "a"="apple", "b"="banana", "c"="cherry")
v
[1] "cherry"
In case of multiple matches, the value of first matching element is returned.
# Select first match and return its value
x <- "a"
v <- switch(x, "a"="apple", "a"="apricot", "a"="avocado")
v
[1] "apple"
Default case
In the case of no match, the unnamed element (if any) is returned. If there are more than one unnamed elements present, an error is raised.
# Select unnamed element in the case of no match
x <- "z"
v <- switch(x, "a"="apple", "b"="banana", "c"="cherry", "grapes")
v
[1] "grapes"
switch() with Numeric Expression
The numeric version of switch() works in a slightly different way. Instead of using names, the return value is determined purely with positional matching (Index).
# Select element by position and return its value
x <- 1
v <- switch(x, "apple", "banana", "cherry")
v
[1] "apple"
x <- 3
v <- switch(x, "apple", "banana", "cherry")
v
[1] "cherry"
If the numeric value is out of range (greater than the number of choices), NULL is returned.
x <- 5
v <- switch(x, "apple", "banana", "cherry")
v
NULL