Rule Engine

This node takes a list of user-defined rules and tries to match them to each row in the input table. If a rule matches, its outcome value is added into a new column. The rules follow a limited SQL-like syntax:

RULE := BEXPR '=>' STRING | NUMBER | COL
BEXPR := '(' BEXPR ')' |
         'NOT' BEXPR |
         'MISSING' COL |
         AEXPR (BINOP BEXPR)?
AEXPR := COL OP COL |
         NUMBER OP COL |
         COL OP NUMBER |
         STRING OP COL |
         COL OP STRING |
         COL LOP STRINGLIST
BOP := 'AND' | 'OR' | 'XOR'
OP := '>' | '<' | '>=' | '<=' | '=' | 'LIKE'
LOP := 'IN'
STRING := '"' [^"]* '"'
NUMBER := [1-9][0-9]*(\.[0-9]+)?
COL := '$' [^$]+ '$'
STRINGLIST := '(' STRING (',' STRING)* ')'

Rules consist of a condition part (antecedant), that must evaluate to true or false, and an outcome (consequent) that is put into the new column if the rule matches. The most simple rule is a comparison between a column and another column, a fixed number or string. The LIKE operator treats the fixed string as a wildcard pattern (with * and ?) as wildcards, the IN operator compares the column value to a list of strings and evaluates to true if at least one value in the list is equal to the column's value. Note that all operators are case-sensitive!

The outcome of a rule can either be a fixed string, a fixed number, or a reference to another column. The type of the outcome column is the common super type of all possible outcomes including the default label. If the outcome of a single rule or the default label is a reference to a column, please check the corresponding option below the text field.

Columns are given by their name surrounded by $, numbers are given in the usual decimal representation. Note that strings must not contain double-quotes.

Rules can (and should) be grouped with brackets because there is not pre-defined operator precedence for the boolean operators (comparison operators always take precedence over boolean operators).

Some example rules:

        $Col0$ > 5 => "Positive"
        $Col0$ = "Active" AND $Col1$" <= 5 => "Outlier"
        $Col0$ LIKE "Market Street*" AND 
            ($Col1 IN ("married", "divorced") 
                OR $Col2$ > 40) => "Strange"
        $Col0$ > 5 => $Col1$