isSingular: Check if a variable only contains a single value
Description
A checkFunction that checks if v only
contains a single unique value, aside from missing values. This
function is intended for use as a precheck in makeDataReport.
Usage
isSingular(v)
isEmpty(v)
Value
A checkResult with three entires:
$problem (a logical indicating whether v contains only one value),
$message (if a problem was found, a message describing which single
value the variable takes and how many missing observations it contains, otherwise
""), and $problemValues (always NULL).
Arguments
v
A variable (vector) to check. All variable types are allowed.