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If-Statements

Use if (and optionally, else) to control the flow of R functions. For example, let x and y be scalar numerical values:

if (x == y) {                # If the logical statement in the ()'s is true,  
  x <- NA                    #  then `x' is changed to `NA' (missing value). 
}
else {                       # The `else' statement tells R what to do if  
  x <- x^2                   #  the if-statement is false.  
}

As with a function, use { and } to define the set of commands associated with each if and else statement. (If you include if statements inside functions, you may have multiple sets of nested curly braces.)