Type Conversion

The as.*() functions convert values from one type to another.

as.numeric("3.5")
as.integer("42")
as.integer(3.99)
as.character(42)
as.logical("TRUE")
as.logical(0)
as.numeric(TRUE)

[1] 3.5
[1] 42
[1] 3
[1] "42"
[1] TRUE
[1] FALSE
[1] 1

• as.integer(3.99) truncates (drops the decimals) rather than rounding. Use round() first if you want the nearest whole number.
• Numbers convert to logicals as 0 → FALSE, anything else → TRUE.

When conversion fails

Text that isn't a valid number becomes NA, with a warning:

as.numeric(c("10", "20", "n/a", "40"))

[1] 10 20 NA 40
Warning message:
NAs introduced by coercion

This is extremely common when importing data: a numeric column containing a stray "n/a" or "-" is read as text. After converting, check how many NAs appeared — they point to the problem cells.

Checking before converting

is.*() functions check a type: is.numeric(), is.character(), is.logical(), is.na().

Common mistakes

• Converting a factor (Level 1's Factors lesson) straight to numbers: as.numeric(factor(c("10", "20"))) gives 1 2 (the category codes), not 10 20. Convert to character first: as.numeric(as.character(f)).