Interactive Session 5B

Logical and comparison operators in R

1. Setup

  • Close, then reopen your project from the earlier session
  • Pull to get any changes since you last worked on it
  • Create a new R script (.R)
  • Save your script as intro-logicals.R

2. Comparison operators

Comparison (or relational) operators compare values and return TRUE or FALSE depending on what you’re comparing.

Less than or greater than

2 < 4
[1] TRUE
5 < 2
[1] FALSE
"A" < "D"
[1] TRUE
"Z" < "Q"
[1] FALSE
"cat" < "dog"
[1] TRUE
"yeti" < "armadillo"
[1] FALSE

So we can see that values can be considered numerically or alphabetically.

This is also true for vectors - each element in a vector will be compared to the corresponding value in the other vector (i.e., the first element in a gets compared to the first element in b). Let’s make a couple vectors and try it out:

dogs <- c(1, 10, 4, 5, 18)
cats <- c(0, 12, 10, 5, 2)

dogs < cats
[1] FALSE  TRUE  TRUE FALSE FALSE

Same for vectors of strings:

dog_names <- c("Teddy", "Khora", "Banjo", "Tallie")
cat_names <- c("Henrietta", "Panda", "Merlin", "Runt")

cat_names < dog_names
[1]  TRUE FALSE FALSE  TRUE

Less than / greater than or equal to

2 <= 5
[1] TRUE
10 >= 10
[1] TRUE

Test alphabetically:

"yeti" <= "yeah"
[1] FALSE

Let’s try it with vectors:

burritos <- c(-4, 10, 1, -5, 9)
tacos <- c(5, 3, 8, -5, 6)

tacos <= burritos
[1] FALSE  TRUE FALSE  TRUE  TRUE

Exact matches with ==

Use == to ask “do these things match?”

5 == 5
[1] TRUE
5 == 4
[1] FALSE
"cat" == "dog"
[1] FALSE
beach <- c(0, 2, 1, 10, 13)
mesa <- c(1, 2, 3, 10, 13)

beach == mesa
[1] FALSE  TRUE FALSE  TRUE  TRUE

Let’s try something interesting:

5 == TRUE
[1] FALSE
5 == FALSE
[1] FALSE
1 == TRUE
[1] TRUE
0 == TRUE
[1] FALSE
0 == FALSE
[1] TRUE

0 recognized as FALSE and 1 recognized as TRUE.

Does NOT match with !=

Use != to ask: does this NOT match that?

5 != 6
[1] TRUE
"cat" != "dog"
[1] TRUE

3. Logical operators

  • &: logical “AND”
  • |: logical “OR”
  • !: logical “NOT”

Logical “AND”

5 < 10 & "cat" < "dog"
[1] TRUE
9 > 4 & 2 < 3
[1] TRUE

An example with vectors:

bananas <- c(10, 21, 12, 15, 22)
apples <- c(9, 18, 16, 20, 30)

apples < bananas & bananas > 20
[1] FALSE  TRUE FALSE FALSE FALSE

Logical “OR”

4 < 10 | 100 < 2
[1] TRUE
5 > 6 | "dog" < "cat" | 10 < 50
[1] TRUE

Logical “NOT”

!"dog" == "cat"
[1] TRUE
!6 == 5
[1] TRUE

4. Push your changes to GitHub

You know the deal!