R Programming - Conditions

Comparison Operators
- equal (==)
- not equal (!=)
- greater or equal to (>=)
- lower or equal to (<=)
Logical Operators
- the and operator (&)
- the or operator (|)
- the not operator (!)
if (Stand-Alone) Statement
else Statement
ifelse Statement

TRUE & TRUE  
TRUE & FALSE
TRUE | FALSE 
!TRUE

2 == 3
5 < 6

c(1,4) >= 6

9 != 8

5 < 6 & 9 != 8

score <- 80
exam_no <- 2

score >= 75 | exam_no == 1

score>=75 & score<90 | exam_no==1

if (Stand-Alone) Statement

The if statement executes a chunk of code if and only if a defined condition is TRUE, which looks something like this:

if(TRUE) message("It was true!")

## It was true!

if(FALSE) message("It wasn't true!")

if(TRUE&FALSE) message("It was true!")

if(TRUE|FALSE) message("It doesn't matter")

## It doesn't matter

a <- 3
num <- 4

if ( a != num ) {
print(a)
}

## [1] 3

a <- 3
num <- 4

if ( a <= num ) {
a <- a ^ 2
print(a)
}

## [1] 9

if (Stand-Alone) Statement

num <- -1

if ( num < 0 ) {
  print("num is negative.")
  print("Don't worry, I'll fix it.") 
  num <- num * -1
  print("Now num is positive.")
}

## [1] "num is negative."
## [1] "Don't worry, I'll fix it."
## [1] "Now num is positive."

num

## [1] 1

if (Stand-Alone) Statement

Try it

Is it in the range ?


x <- 6
y <- 2

if ( x > 3 & x == 7 ) {
  print("It is in the range")
  z <- x + y
  print(z)
}

Is it in the range ?

x <- 6
y <- 2

if ( x > 3 & x <= 7 ) {
  print("It is in the range")
  z <- x + y
  print(z)
}

## [1] "It is in the range"
## [1] 8

Try it

You have a fruit which is yellow.

Is that a banana?

Or an orange ?

banana <- "yellow"
my_fruit <- "yellow"

if ( my_fruit == banana ) {
  print("Your fruit might be a banana")
}

orange <- "orange"
my_fruit <- "yellow"

if ( my_fruit == orange ) {
  print("Your fruit is not a banana")
}

else - Statement

If you want something different to happen when the condition is FALSE, you can add an else declaration.

if(FALSE)
    {
      message("This won't execute...")
} else
    {
      message("but this will.")
}

## but this will.

a <- 3.5
b <- 0.5

if (a <= 0.5) {
  c <- b + 1
  print(c)
} else {
  c <- b
  print(c)
}

## [1] 0.5

Let’s say we have two conditions. Rainy or Shiny.

And you have recorded 4 mm precipitation.

weather <-       # mm           # fill this number

if ( ) {                        # fill this condition, using weather
  print("it is rainy")
} else {
  print("it is shiny")
}

Report the weather. Is it rainy ?

Let’s say we have two conditions. Rainy or Shiny.

And you have recorded 4 mm precipitation.

weather <- 4      # mm              # fill this number

if ( weather > 0 ) {                # fill this condition, using weather
  print("it is rainy")              
} else {
  print("it is shiny")
}

## [1] "it is rainy"

-else - and -else if- Statement

If your situation has more than two mutually exclusive cases, use else and if statements together.

a <- 1                  # team 'a' has 1 goal
b <- 1                  # team 'b' has 1 goal

if (a > b) { 
  print("A wins!")
} else if (a < b) { 
  print("B wins!")
} else {
  print("Tie.")
}

## [1] "Tie."

What do you gonna do ? Eating, Sleeping, or Reading?

When do you want to read ?

When you are hungry, or sleepy. No.
When you are not hungry and sleepy. Yes.

So, start to think about your feelings about sleeping or eating to decide whether reading or not.