fcase: fcase

In data.table: Extension of `data.frame`

fcase

Description

fcase is a fast implementation of SQL CASE WHEN statement for R. Conceptually, fcase is a nested version of fifelse (with smarter implementation than manual nesting). It is comparable to dplyr::case_when and supports bit64's integer64 and nanotime classes.

Usage

  fcase(..., default=NA)

Arguments

...	A sequence consisting of logical condition (when)-resulting value (value) pairs in the following order when1, value1, when2, value2, ..., whenN, valueN. Logical conditions when1, when2, ..., whenN must all have the same length, type and attributes. Each value may either share length with when or be length 1. Please see Examples section for further details.
default	Default return value, NA by default, for when all of the logical conditions when1, when2, ..., whenN are FALSE or missing for some entries.

Details

fcase evaluates each when-value pair in order, until it finds a when that is TRUE. It then returns the corresponding value. During evaluation, value will be evaluated regardless of whether the corresponding when is TRUE or not, which means recursive calls should be placed in the last when-value pair, see Examples.

default is always evaluated, regardless of whether it is returned or not.

Value

Vector with the same length as the logical conditions (when) in ..., filled with the corresponding values (value) from ..., or eventually default. Attributes of output values value1, value2, ...valueN in ... are preserved.

See Also

fifelse

Examples

x = 1:10
fcase(
	x < 5L, 1L,
	x > 5L, 3L
)

fcase(
	x < 5L, 1L:10L,
	x > 5L, 3L:12L
)

# Lazy evaluation example
fcase(
	x < 5L, 1L,
	x >= 5L, 3L,
	x == 5L, stop("provided value is an unexpected one!")
)

# fcase preserves attributes, example with dates
fcase(
	x < 5L, as.Date("2019-10-11"),
	x > 5L, as.Date("2019-10-14")
)

# fcase example with factor; note the matching levels
fcase(
	x < 5L, factor("a", levels=letters[1:3]),
	x > 5L, factor("b", levels=letters[1:3])
)

# Example of using the 'default' argument
fcase(
	x < 5L, 1L,
	x > 5L, 3L,
	default = 5L
)

# fcase can be used for recursion, unlike fifelse
# Recursive function to calculate the Greatest Common Divisor
gcd_dt = function(x,y) {
  r = x%%y
  fcase(!r, y, r, gcd_dt(x, y)) # Recursive call must be in the last when-value pair
}
gcd_dt(10L, 1L)

data.table documentation built on Aug. 8, 2025, 6:20 p.m.