Logical Values and Comparisons

A logical value is TRUE or FALSE. Comparisons produce logicals — and, like everything in R, they work on whole vectors.

age <- 20
age > 18
age == 21
age != 21

ages <- c(12, 25, 37, 8)
ages >= 18

[1] TRUE
[1] FALSE
[1] TRUE
[1] FALSE  TRUE  TRUE FALSE

Combining conditions

ages <- c(12, 25, 37, 8, 70)

ages >= 18 & ages < 65
ages < 13 | ages > 65
!(ages > 30)

[1] FALSE  TRUE  TRUE FALSE FALSE
[1]  TRUE FALSE FALSE  TRUE  TRUE
[1]  TRUE  TRUE FALSE  TRUE FALSE

• & (and), | (or), and ! (not) work element by element.
• && and || work on single values and are used in if conditions (next lessons).

Counting with logicals

TRUE counts as 1 and FALSE as 0, so sum and mean answer "how many" and "what proportion":

ages <- c(12, 25, 37, 8, 70)
sum(ages >= 18)
mean(ages >= 18)
any(ages > 65)
all(ages > 0)

[1] 3
[1] 0.6
[1] TRUE
[1] TRUE

This is an everyday data-analysis idiom: "60% of the people are adults".

Common mistakes

• Writing T and F instead of TRUE and FALSE. They work, but T and F can be overwritten as ordinary variables — always write the full words.
• Using = instead of == in a comparison.