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In Wrangle transformations that support use of regex patterns, you may need to specify capture groups. A capture group is a pattern that describes a set of one or more characters that constitute a match.

  • These patterns are described using regular expression syntax.  Trifacta Wrangler Enterprise implements a version of regular expressions based off of RE2 and PCRE regular expressions.

This section contains information on how special capture group references are managed.

Dollar sign in replace transform

The dollar sign ($) is used as a form of escape character in the with parameter of the replace transform. This pattern identifies the replacement string.

In the table below, you can review how these replacement patterns are supported across the running environments.

PatternDescriptionOn PhotonOn Hadoop
$$Inserts a $ in the replacement value.YesYes
$n or
$nn 
For non-negative digits n, this pattern inserts the nth parameterized sub-match string, provided that the first argument was a regex object. Yes Yes

 

Examples

In the following example, the MyColumn column contains the value foobar in all rows.

source valuereplace transformreplacement
foobar
replace col:MyColumn with:'$$f' on:'f'
$foobar
foobar
replace col:MyColumn with:'$2' on:`(f)(o)(o)bar`

Note that the on parameter is a Trifacta® pattern.

o

 

Positive and Negative Lookaheads

In regular expressions, you can use positive and negative lookahead capture groups to capture content that is conditionally followed or not followed by a specified capture group.

TypeExample expression 
Positive lookahead
/q(?u)/
Capture the letter q only when it is followed by the letter u. Letter u is not captured.
Negative lookahead
/q(?!u)/
Capture the letter q when it is not followed by the letter u. Letter u is not captured.

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