Skip to content

Latest commit

 

History

History
370 lines (248 loc) · 7.07 KB

chapter2_08_conditionalstatements.md

File metadata and controls

370 lines (248 loc) · 7.07 KB
title type
Conditional Statements
slides

Relational operators

Relational operators, or comparators, are operators which help us see how one R object relates to another. The relational operators in R are:

  • < for less than
  • > for greater than
  • <= for less than or equal to
  • >= for greater than or equal to
  • == for equal to each other
  • != not equal to each other

You can use these command on scalar.

For example,

8 > 1
## [1] TRUE

8 > 1 return TRUE since 8 is larger than 1.

8 ==1
## [1] FALSE

8 == 1 return FALSE since 8 is not equal to 1.

Notes:

Relational operators:

  • < for less than
  • > for greater than
  • <= for less than or equal to
  • >= for greater than or equal to
  • == for equal to each other
  • != not equal to each other

These command also extends to vectors.

For example,

c(0,5,100) == 5
## [1] FALSE  TRUE FALSE

Both the first and the last entry evaluates to FALSE and only the second entry returns TRUE (equal to 5).

Notes:

Relational operators:

  • < for less than
  • > for greater than
  • <= for less than or equal to
  • >= for greater than or equal to
  • == for equal to each other
  • != not equal to each other

These command also extends to vectors. It tests for every element of the vector if the condition stated by the comparison operator is TRUE or FALSE.

You can see that both the first and the last entry evaluates to FALSE and only the second entry returns TRUE since the second entry is equal to 5.

Now if instead we do

c(0,5,100) >= 5
## [1] FALSE  TRUE  TRUE

You can see the output changed since 100 is also greater than or equal to 5.

If we change our code into

c(0,5,100) < 5
## [1]  TRUE FALSE FALSE

You can see the output changed where the second entry is also FALSE since 5 is not strictly less than 5.

Note that R also support element-wise comparison if we put a relational operator between two vectors:

c(2,4,6) < c(3,5,7)
## [1] TRUE TRUE TRUE

Logical opeators

Next, you can change or combine the results of relational comparisons using:

  • the AND (&) operator
  • the OR (|) operator
  • the NOT (!) operator

Notes:

Now you know how to use relational operators in R. Next, what if you want to change or combine the results of these comparisons? In R, you can do this using the AND (&), the OR (|), and the NOT (!) operator.

the AND (&) operator

The AND operator typically takes two logical values and returns TRUE only if both the logical values are TRUE themselves.

For example, if we check the entries of the following vector x is greater than 2 AND less than 6, we expect TRUE for the three entries in the middle.

x = c(1,2,3,4,5,6,7)
(x>2)&(x<6)
## [1] FALSE FALSE  TRUE  TRUE  TRUE FALSE FALSE

the OR (|) operator

The OR operator (|) works similarly, but the difference is that only at least one of the logical values it uses should be equal to TRUE for the entire OR operation to evaluate to TRUE.

For example,

x = c(1,2,3,4,5,6,7)
(x>4)|(x<2)
## [1]  TRUE FALSE FALSE FALSE  TRUE  TRUE  TRUE

the NOT (!) operator

The NOT operator negates the logical value it's used on.

Say we want to check if an object a is a numeric, where a is actually a string rain, we expect the output to be FALSE.

a <- "rain"
is.numeric(a)
## [1] FALSE

#if the input is actually a number
is.numeric(100)
## [1] TRUE

Notes:

The NOT operator negates the logical value it's used on.

For example, the built-in R function, is is.numeric() checks if an R object is a numeric.

Say we want to check if an object a is a numeric, where a is actually a string rain, we expect the output to be FALSE.

Consider also object b is a number, then the expected output is TRUE.

If we, instead, use !is.numeric(a) to check if a is, the output is now TRUE.

!is.numeric(a)
## [1] TRUE

And when we run !is.numeric(100) in R, the output would be FALSE.

!is.numeric(100)
## [1] FALSE

Conditional statements

Now we are ready to learn about conditional statements:

  • if
  • else
  • else if

Notes:

Now we are ready to learn about conditional statements: if, else, else if.

These conditional statements are very useful in data analysis since often we want to treat the data differently depending on certain conditions.

if statement

The syntax of an if statement looks like this:

if (condition) {
  do_this
}

So if the condition is evaluated to be TRUE, the code included in the curly bracket (do_this) will be executed.

For example, customer_rating contains a rating (out of 5) from a customer dined in a restaurant.

We consider a customer to be happy if the rating is greater than or equal to 4.

customer_rating = 4
if (customer_rating >= 4){
  print("Customer is happy!")
}
## [1] "Customer is happy!"

else statement

You can only use an else statement together with an if statement.

The syntax of an else statement looks like this:

if (condition) {
  do_this
} else {
  do_this_instead
}

It's important that the syntax else is on the same line as the closing bracket of the if part!

Note:

You can only use an else statement together with an if statement.

The else statement does not require a condition.

The code that comes under the else statement is executed if all of the if statements evaluated to be FALSE.

So if the condition is evaluated to be TRUE, the code included in the first curly bracket (do_this) will be executed. Otherwise, the code included in the second curly bracket (do_this_instead) will be executed.

It's important that the syntax else is on the same line as the closing bracket of the if part!

For example, we would like to be alerted if a customer is not happy.

customer_rating = 2
if (customer_rating >= 4){
  print("Customer is happy!")
} else { 
  print("Attention - unhappy customer!")
}
## [1] "Attention - unhappy customer!"

else if statement

The else if statement allows you to further customize your control structure.

The syntax of an else if statement looks like this:

if (condition1) {
  action1
} else if (condition2) {
  action2
} else if (condition3) {
  action3
} else {
  action4
}

Note:

The else if statement allows you to further customize your control structure. You can add as many else if statements as you like such that you can customize the action of your code depending on the conditions.

For example, we would like to distinguish between:

  • happy customer (with rating 4 or above),
  • neutral customer (rating to be less than 4 but higher than 2)
  • unhappy customer (rating not more than 2).
customer_rating = 3
if (customer_rating >= 4){
  print("Customer is happy!")
} else if (customer_rating <= 2){ 
  print("Attention - unhappy customer!")
} else {
  print("Neutral customer.")
}
## [1] "Neutral customer."