if Statements

In this lesson, we will learn about if statements.

We'll cover the following

While writing a program, you may have to change the flow of the code depending on certain conditions and inputs.

For example, if we are dealing with numbers in our program we may want to print “positive” if the number we received is a positive integer.

Here, we will have to write a condition that tells us to print “positive” if we receive a positive number.

For such a situation, we need Conditional statements.

What are Conditional Statements?

Conditional statements are used in programming languages to perform different computations or actions depending on whether a certain condition is met.

Let’s have a look at an example:

Diagram to show how code flow is altered.
Diagram to show how code flow is altered.

The above diagram is an example of the if statement. It is called a flow chart. Here, the diamond boxes usually contain conditions and the rectangular boxes contain statements. The arrows show the flow of execution.

What is an if statement?

An if statement consists of a Boolean expression that when satisfied performs certain actions.

x <- 5
if(x > 0) # condition for checking positive numbers (all positive numbers are greater than 0)
{
  print("Positive number")
}
Conditional statement is satisfied

Notice, we have used a Relational Operator greater than > that returns TRUE or FALSE depending on the value of x>0x > 0. This, in turn, determines whether or not to print “positive”.

Conditional statements allow programmers to deal with inputs or features of the data depending on different R expressions.

Let’s look at another example:

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myVector <- c(1, 2, 3, 5)
testNumber <- 4
if(!testNumber %in% myVector)
{
  print("Not Found!")
}

Let’s breakdown the condition !testNumber %in% myVector Line number 4.

Conditional Statement Breakdown:

  1. testNumber %in% myVector checks whether the number contained in the variable testNumbertestNumber is present in myVectormyVector. In this case, whether the number 44 is present in the vector.
  2. For this particular code snippet, the answer is FALSE.
  3. Now, the symbol ! takes the NOT of the result of testNumber %in% myVector.
  4. In our case, it takes NOT of FALSE which is TRUE.
  5. Hence, our conditional statement is satisfied. We can now proceed to the statement.
print("Not Found!")