get_ternary_class_id: Get ternary class id
Description
Helper function that checks if a value surpasses the given
threshold either positively, negatively or not at all and returns
a value indicating in which class (i.e. interval) it belongs.
Usage
get_ternary_class_id(value, threshold)
Value
an integer. There are 3 cases:
Arguments
- value
numeric
- threshold
numeric