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In general a dispatch table or class/object abstraction (using dynamic method over-rides) is considered preferable to chains of ''if ... elif ... elif ...'' in Python programming.
=={{header|RRacket}}==
===if-else===
[http://docs.racket-lang.org/reference/if.html#%28form._%28%28quote._~23~25kernel%29._if%29%29 If-expressions]
<lang R>#Single line example
in Racket must have both branches
#x is assumed to be scalar
<lang Racket>
if(x < 3) message("x is less than 3") else if(x < 5) message("x is greater than or equal to 3 but less than 5") else message("x is greater than or equal to 5")
(if (< x 10)
#Block example
"small"
if(x < 3)
"big")
{
</lang>
x <- 3
warning("x has been increased to 3")
} else
{
y <- x^2
}
#It is important that the else keyword appears on the same line as the closing '}' of the if block.</lang>
===ifelse===
<lang r>#ifelse is a vectorised version of the if/else flow controllers, similar to the C-style ternary operator.
x <- sample(1:10, 10)
ifelse(x > 5, x^2, 0)</lang>
===switch===
See [http://cran.r-project.org/doc/manuals/R-lang.html#switch doc] for R switch statement.
<lang r># Character input
calories <- function(food) switch(food, apple=47, pizza=1500, stop("food not known"))
calories("apple") # 47
calories("banana") # throws an error
# Numeric input
alphabet <- function(number) switch(number, "a", "ab", "abc")
alphabet(0) # null response
alphabet(1) # "a"
alphabet(2) # "ab"
alphabet(3) # "abc"
alphabet(4) # null response
# Note that no 'otherwise' option is allowed when the input is numeric.</lang>
=={{header|Retro}}==
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