R If ... Else
Conditions and If Statements
R supports the usual logical conditions from mathematics:
| Operator | Name | Example | Try it |
|---|---|---|---|
| == | Equal | x == y | Try it » |
| != | Not equal | x != y | Try it » |
| > | Greater than | x > y | Try it » |
| < | Less than | x < y | Try it » |
| >= | Greater than or equal to | x >= y | Try it » |
| <= | Less than or equal to | x <= y | Try it » |
These conditions can be used in several ways, most commonly in "if statements" and loops.
An "if statement" is written with the if keyword, and it is used to specify a block of code to be executed if a condition is TRUE:
In this example we use two variables, a and b, which are used as a part of the if statement to test whether b is greater than a. As a is 33, and b is 200, we know that 200 is greater than 33, and so we print to screen that "b is greater than a".
R uses curly brackets { } to define the scope in the code.
Else If
The else if keyword is R's way of saying "if the previous conditions were not true, then try this
condition":
Example
a <- 33
b <- 33
if (b > a) {
print("b is greater than a")
} else if (a == b) {
print ("a and b are equal")
}
Try it Yourself »
In this example a is equal to b, so the first condition is not true, but the else if condition is true, so we
print to screen that "a and b are equal".
You can use as many else if statements as you want in R.
If Else
The else keyword catches anything which isn't caught by the preceding conditions:
Example
a <- 200
b <- 33
if (b > a) {
print("b is greater than a")
} else if (a == b) {
print("a and b are equal")
} else {
print("a is greater than b")
}
Try it Yourself »
In this example, a is greater than b, so the first condition is not true, also the else if condition is not true, so we go to the else condition and print to screen that "a is greater than b".
You can also use else without
else if:
Example
a <- 200
b <- 33
if (b > a) {
print("b is greater than a")
} else {
print("b is not greater than a")
}
Try it Yourself »
Nested If Statements
You can also have if statements inside
if statements, this is called nested
if statements.
Example
x <- 41
if (x > 10) {
print("Above ten")
if (x >
20) {
print("and also above 20!")
} else {
print("but not above 20.")
}
} else {
print("below
10.")
}
Try it Yourself »
AND
The & symbol (and) is a logical operator, and is used to combine conditional statements:
Example
Test if a is greater than b, AND if c is greater than a:
a <- 200
b <- 33
c <- 500
if (a > b & c > a){
print("Both conditions are true")
}
Try it Yourself »
OR
The | symbol (or) is a logical operator, and is used to combine conditional statements:
Example
Test if a is greater than b, or if c is greater than a:
a <- 200
b <- 33
c <- 500
if (a > b | a > c){
print("At
least one of the conditions is true")
}
Try it Yourself »
