CDE

Task/Conditional-structures/R/conditional-structures-1.r

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+#Single line example
+ #x is assumed to be scalar
+ 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")
+#Block example
+ if(x < 3)
+ {
+    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.

Task/Conditional-structures/R/conditional-structures-2.r

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+#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)

Task/Conditional-structures/R/conditional-structures-3.r

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+# 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.