Control Structure

Learning objectives

• Questions:

  • How do I use If-Then-Else structure?

  • How do I use For loops?

  • How do I use While loops?

• Objectives:

  • Write conditional statement with if...else and elseif()

  • Write and understand for() loop

• Keypoints:

  • “Use if and else”

  • “Use for loop “

if-else

• if

if (condition){
  do task
}

• if…else

if (condition1){
  do task 1
} else {
  do the rest
}

• if…elseif…else

if (condition1){
  do task 1
} else if (condition2) {
  do task 2
} else {
  do the rest
}

• ifelse()

ifelse(condition,action if true,action if false)

• Examples

a <- 5
if (a>3){
  print("a is bigger than 3")
}

a <- 5
if (a>3){
  print("a is bigger than 3")
} else {
  print("a is NOT bigger than 3")
}

a <- 5
if (a>3){
  print("a is bigger than 3")
} else if (a==3) {
  print("a equals to 3")
} else {
  print("a is less than 3")
}

a <- 5
response <- ifelse(a>3,"a is bigger than 3","a is not bigger than 3")
response
class(response)

For Loop

• Full Syntax:

for (iterator in sequence){
  do task
}

• Example:

for (i in 1:5){
  print(i)
}

for (i in seq(1,5,2)){
  print(i)
}

• Short Syntax

for (i in 1:5) print(i)

for (i in seq(1,5)) print(letters[i])

While Loop

• Syntax

while (this condition is true){
  do a task
}

• Example:

a <- 1
while (a<5){
  print(a)
  a <- a+1
}