How can I do multiple replace using a shared backreference? - regex

Question

I have a need to do some data-transformation for data load compatibility. The nested key:value pairs need to be flattened and have their group id prepended to each piece of child data.
I've been trying to understand the page at
Repeating a Capturing Group vs. Capturing a Repeated Group but can't seem to wrap my head around it.
My expression so far:
"(?'group'[\w]+)": {\n((\s*"(?'key'[^"]+)": "(?'value'[^"]+)"(?:,\n)?)+)\n},?
Working sample: https://regex101.com/r/Wobej7/1
I'm aware that using 1 or more intermediate steps would simplify the process but at this point I want to know if it's even possible.
Source Data Example:
"g1": {
"k1": "v1",
"k2": "v2",
"k3": "v3"
},
"g2": {
"k4": "v4",
"k5": "v5",
"k6": "v6"
},
"g3": {
"k7": "v7",
"k8": "v8",
"k9": "v9"
}
Desired transformation:
{"g1","k1","v1"},
{"g1","k2","v2"},
{"g1","k3","v3"},
{"g2","k4","v4"},
{"g2","k5","v5"},
{"g2","k6","v6"},
{"g3","k7","v7"},
{"g3","k8","v8"},
{"g3","k9","v9"}

Answer 1

TL; DR
Step 1
Search for:
("[^"]+"):\s*{[^}]*},?\K
Replace with \1
Live demo
Step 2
Search for:
(?:"[^"]+":\s*{|\G(?!\A))\s*("[^"]+"):\s*((?1))(?=[^}]*},?((?1)))(?|(,)|\s*}(,?).*\R*)
Replace with:
{\3,\1,\2}\4\n
Live demo
Whole philosophy
This is not going to be a one-liner regex solution for different reasons. The most important one is we can neither store a part of a match for later referring nor are able to do infinite lookbehinds in PCRE. But fortunately most of similar problems could be done in two steps.
Very first step should be moving group name to end of {...} block. This way we can have group name each time we want to transform our matches into a single line output.
("[^"]+"):\s*{[^}]*},?\K
( Start of capturing group #1
"[^"]+" Match a group name
) End of CG #1
:\s*{ Group name should precede bunch of other characters
[^}]*},? We have to go further up to end of block
\K Throw away every thing matched so far
We have our group name held in first capturing group and have to replace whole match with it:
\1
Now a block like this:
"g1": {
.
.
.
},
Appears like this one:
"g1": {
.
.
.
},"g1"
Next step is to match key:value pairs of each block beside capturing recent added group name at the end of block.
(?:"[^"]+":\s*{|\G(?!\A))\s*("[^"]+"):\s*((?1))(?=[^}]*},?((?1)))(?|(,)|\s*}(,?).*\R*)
(?: Start of a non-capturing group
"[^"]+" Try to match a group name
:\s*{ A group name should come after bunch of other characters
| Or
\G(?!\A) Continue from previous match
) End of NCG
\s*("[^"]+"):\s*((?1)) Then try to match and capture a key:value pair
(?=[^}]*},?((?1))) Simultaneously match and capture group name at the end of block
(?|(,)|\s*}(,?).*\R*) Match remaining characters such as commas, brace or newlines
This way in each single successful try of regex engine we have four captured data that their order is the key:
{\3,\1,\2}\4\n
\3 Group name (that one added at the end of block)
\1 Key
\2 Value
\4 Comma (may be there or may not)