? {rtern}

Succinct conditional evaluation and assignment

Description

? is an in-line if/else operator

Usage

lhs ? rhs

Arguments

lhs

A logical expression, vector or matrix.

rhs

A pair of values separated by a colon i.e. value_if_true : value_if_false.

Details

The syntax for ? is as follows:

condition ? value_if_true : value_if_false

The condition is evaluated TRUE or FALSE as a Boolean expression. On the basis of the evaluation of the Boolean condition, the entire expression returns value_if_true if condition is true, but value_if_false otherwise. In the case where the condition is a vector/matrix of Boolean values, the function returns a vector/matrix where each element is either value_if_true or value_if_false based on the truthiness of the elements of the object on the left-hand side. In these cases the behaviour of ⁠?⁠ mimics ifelse.

Who has time for if/else?

Value

One of the values in rhs, depending on the truthiness of lhs.

Examples

# Conditional evaluation
4 > 3 ? "it_was_true":"it_was_false"
# > "it_was_true"

FALSE ? "it_was_true":"it_was_false"
# > "it_was_false"

# Vectorised evaluation
c(4, 2) < 3 ? "it_was_true":"it_was_false"
# > "it_was_false" "it_was_true"

# Conditional assignment with `<-`
x <- 4 > 3 ? "it_was_true":"it_was_false"
x
# > "it_was_true"

# Conditional assignment with `=`
y <- 3 > 4 ? "it_was_true":"it_was_false"
y
# > "it_was_false"

# Chaining `?` statements
z <- FALSE ? "true":(FALSE ? "false,true":(TRUE ? "false,false,true":"all false"))
z
# > "false,false,true"