Patterns - Aster Analytics

The value of the Pattern argument specifies the sequence of rows for which the function searches. You compose the pattern definition, pattern, with symbols (which you define in the Symbols argument), operators, and parentheses. In the pattern definition, symbols represent rows. You can combine symbols with pattern operators to define simple or complex patterns of rows for which to search.

The following table lists and describes the basic pattern operators, in decreasing order of precedence. In the table, A and B are symbols that have been defined in the Symbols argument.

A

A.

A?

A*

A+

A.B

A|B

The nPath function uses greedy pattern matching. That is, it finds the longest available match when matching patterns specified by nongreedy operators. For more information, see Greedy Pattern Matching.

Example:

A.(B|C)+.D?.X*.A

The preceding pattern definition matches any set of rows whose first row meets the definition of symbol A, followed by a nonempty sequence of rows, each of which meets the definition of either symbol B or C, optionally followed by one row that meets the definition of symbol D, followed by any number of rows that meet the definition of symbol X, and ending with a row that meets the definition of symbol A.

You can use parentheses to define precedence rules. Parentheses are recommended for clarity, even where not strictly required.

To indicate that a sequence of rows must start or end with a row that matches a certain symbol, use the start anchor (^) or end anchor ($) operator.

^A

A$

Subpattern operators let you specify how often a subpattern must appear in a match. You can specify a minimum number, exact number, or range. In the following table, X represents any pattern definition composed of symbols and any of the previously described pattern operators.

(X){a}

(X){a,}

(X){a,b}