Create a factor with levels ordered by a separate ordering vector

Converts a character vector or factor into a factor where the level order is determined by a second integer-like vector containing the corresponding order values.

Usage

factor_by_order(x, y, ordered = FALSE)

Arguments

x

(character or factor)
A vector to be converted to a factor.

y

(integerish)
A vector defining the order of levels in x. Must have the same length as x.

ordered

(logical(1))
Indicates whether the result should be an ordered factor. Defaults to FALSE.

Value

A factor created from x, with levels ordered according to y. Attributes of x other than class and levels are preserved. If ordered = TRUE, an ordered factor is returned. If x is empty or consists entirely of missing values, a factor with no levels is returned.

Details

The values in x and y must define a bijection between the unique non-missing values: each unique value in x must correspond to exactly one unique value in y, and vice versa. Missing values are handled separately: NA values in x and y must occur at the same positions. Missing values are not included as factor levels.

If x is already a factor containing unobserved (unused) levels, these unobserved levels will be dropped in the resulting factor.

Author

WW

Examples

factor_by_order(c("A", "A", "B"), c(1, 1, 2))
#> [1] A A B
#> Levels: A B

factor_by_order(c("A", "A", "B"), c(1, 1, 2), ordered = TRUE)
#> [1] A A B
#> Levels: A < B

factor_by_order(c("A", "A", "B"), c(2, 2, 1))
#> [1] A A B
#> Levels: B A

factor_by_order(c("A", "A", "B", NA), c(1, 1, 2, NA))
#> [1] A    A    B    <NA>
#> Levels: A B

if (FALSE) { # \dontrun{
factor_by_order(c("A", "A", "B", NA), c(1, 2, 2, 4))
} # }