Lesson 5 R Control Structures and Functions 2024 Notes.pptx

CMT 429
Introduction to Data Science
Lecturer: David Gichohi
Lesson 5: R Control Structures and
Functions

CMT 409- Introdcution to Data Science 2
Content
• Conditional Statements
If
Else If
If Else
Nested If
AND/OR
• Loops
While
For
(Break, Next)
• Functions

If statement
• Written with the if keyword, and it is used to specify a block of code
to be executed if a condition is TRUE.
a <- 33
b <- 200
if (b > a) {
print("b is greater than a")
}

Else if statement
• "if the previous conditions were not true, then try this condition“
a <- 33
b <- 33
if (b > a) {
} else if (a == b) {
print ("a and b are equal")
}

If Else Statement
• The else keyword catches anything which isn't caught by the
preceding conditions.
a <- 200
b <- 33
if (b > a) {
} else {
print("b is not greater than a")
}

Nested If
• if statements inside if statements
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.")
}

While Loop
• Example: Print i as long as i is less than 6:
i <- 1
while (i < 6) {
print(i)
i <- i + 1
}
• With the break statement, we can stop the loop even if the while condition is
TRUE:
i <- 1
while (i < 6) {
print(i)
i <- i + 1
if (i == 4) {
break
}
}
• With the next statement, we can skip an iteration without terminating the
loop
(NB: Replace ‘break’ with ‘next’ in above example.)

For Loop
• A for loop is used for iterating over a sequence
for (x in 1:10) {
print(x)
}
• With the for loop we can execute a set of statements, once for each item in a vector, array, list, etc.
• Print every item in a list:
fruits <- list("apple", "banana", "cherry")
for (x in fruits) {
print(x)
}
• Print the number of dices:
dice <- c(1, 2, 3, 4, 5, 6)
for (x in dice) {
print(x)
}

Nested Loop
• It is possible to place a loop inside another loop.
• Example: Print the adjective of each fruit in a list:
adj <- list("red", "big", "tasty")
fruits <- list("apple", "banana", "cherry")
for (x in adj) {
for (y in fruits) {
print(paste(x, y))
}
}

Functions
• A function is a block of code which only runs when it is called.
• You can pass data, known as parameters, into a function.
• A function can return data as a result.
• To create a function, use the function() keyword.
• To call a function, use the function name followed by ().
# create a function with the name my_function
my_function <- function(){
print("Hello World!")
}
my_function() # call the function named my_function

Function Arguments/Parameters
• Information can be passed into functions as arguments.
• Arguments are specified after the function name, inside the
parentheses.
• You can add as many arguments as you want, just separate them with
a comma.
• A parameter is the variable listed inside the parentheses in the
function definition while an argument is the value that is sent to the
function when it is called.
• To let a function return a result, use the return() function.

Function Examples
1. my_function <- function(fname) {
paste(fname, "Griffin")
}
my_function("Peter")
my_function("Lois")
my_function("Stewie")
2. my_function <- function(fname, lname) {
paste(fname, lname)
}
my_function("Peter", "Griffin")
3. my_function <- function(country = "Norway") {
paste("I am from", country)
}
my_function("Sweden")
my_function("India")
my_function() # will get the default value, which is Norway
4. my_function <- function(x) {
return (5 * x)
}
print(my_function(3))

Assignments
• Using AND/OR symbols, write a program that combine conditional
statements.
• Write a program demonstrate If .. Else Combined with a While Loop.
• Write a recursive function to compute factorial of a number.

Lesson 5 R Control Structures and Functions 2024 Notes.pptx

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