Capture Group References

In

D toc

Excerpt

In

D s lang

transformations that support use of 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 matches can be programmatically referenced in replacement values.

These patterns are described using regular expression syntax.
D s product
implements a version of regular expressions based off of RE2 and PCRE regular expressions.

...

D trans

RawWrangle	true
p03Value	'First Word\:$1'
Type	step
WrangleText	replace col:* on:`{start}(%+) ` with:'First Word\:$1'
p01Name	ColumnColumns
p01Value	*All
p02Name	Find
p02Value	`{start}(%+) `
p03Name	Replace with
SearchTerm	Replace text or pattern

...

Reference

Description

{start}

A

d-s-itemlang

item	pattern

reference to the start of the tested value.

(%+)

Matches on one or more characters of any time.

Info
NOTE: The parentheses indicate that this set of characters is a capture group.

Last character in the matching pattern is an empty space.

...

D trans

RawWrangle	true
p03Value	'First Word\:$1'
Type	step
WrangleText	replace col:* on:`{start}(%+) ( \|{end})` with:'First Word\:$1'
p01Name	ColumnColumns
p01Value	*All
p02Name	Find
p02Value	`{start}(%+) ( \|{end})`
p03Name	Replace with
SearchTerm	Replace text or pattern

...

Reference

Description

first character in the second capture group is an empty space.

|

Logical OR, which means that the capture group matches on either the empty space or the following value, which is a reference to the end of the tested value.

{end}

A

d-s-

item

lang

item	pattern

reference to the end of the tested value.

...

D trans

RawWrangle	true
p03Value	'Second Word\:$2'
Type	step
WrangleText	replace col:* on:`{start}(%+) (%+)( \|{end})` with:'Second Word\:$2'
p01Name	ColumnColumns
p01Value	*All
p02Name	Find
p02Value	`{start}(%+) (%+)( \|{end})`
p03Name	Replace with
SearchTerm	Replace text or pattern

...

source value Replace transformation replacement

foobar

D trans

RawWrangle	true
p03Value	'$$f'
Type	step
WrangleText	replace col:MyColumn with:'$$f' on:'f'
p01Name	Column
p01Value	MyColumn
p02Name	Find
p02Value	'f'
p03Name	Replace with
SearchTerm	Replace text or pattern

$foobar

foobar

D trans

RawWrangle	true
p03Value	'$2'
Type	step
WrangleText	replace col:MyColumn with:'$2' on:`(f)(o)o(b)ar`
p01Name	Column
p01Value	MyColumn
p02Name	Find
p02Value	`(f)(o)o(b)ar`
p03Name	Replace with
SearchTerm	Replace text or pattern

Note that the on parameter is a

d-s-itemlang

item	pattern	r	true

.

o

Positive and Negative Lookaheads

...

Type Example expression

Positive lookahead

Code Block
/q(?u)/

Capture the letter q only when it is followed by the letter u. Letter u is not captured.

Negative lookahead

Code Block
/q(?!u)/

Capture the letter q when it is not followed by the letter u. Letter u is not captured.

D s also

inCQL	true
label	((label = "group") OR (label = "references"))

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Positive and Negative Lookaheads