Regex Match Group Presence Table

Report explicit JSON match-group presence where null means unmatched and empty string means a present empty capture; ragged match groups are retained.

Description

Report explicit JSON match-group presence where null means unmatched and empty string means a present empty capture; ragged match groups are retained.

An unmatched capture differs from a capture that matched an empty string. A null representation preserves that distinction.

When to use this tool

Report explicit JSON match-group presence where null means unmatched and empty string means a present empty capture; ragged match groups are retained.

Prepare the supplied groupsJson fields for this operation.
Compare the complete example with the representation used by your own input before carrying the result into another step.

How to use the tool and how it works

Enter groupsJson. Use the exact text syntax, units and index conventions explained below.
Run the tool. If input validation fails, correct the supplied fields before interpreting any result.
Read result.presence. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.

Parse groupsJson as an array of capture lists containing only strings or null. Map every non-null value, including an empty string, to true and null to false.^[1]

Input field	Meaning and representation	Accepted input
groupsJson	JSON text, entered as one text field. The decoded structure is illustrated below; it is not a separate file.	Text

For the JSON text fields, the following decoded structures show the example records before they are serialized into input strings. Keep field names, list nesting and value types as shown.

json

[
  {
    "field": "groupsJson",
    "decoded": [
      [
        "",
        null,
        "a"
      ],
      [
        null,
        "b"
      ]
    ]
  }
]

Output field	Interpretation
result	Object containing the named outputs below.
result.presence	The presence list in the ordering and representation described above.

json

{
  "input": {
    "groupsJson": "[[\"\",null,\"a\"],[null,\"b\"]]"
  },
  "output": {
    "result": {
      "presence": [
        [
          true,
          false,
          true
        ],
        [
          false,
          true
        ]
      ]
    }
  }
}

Limitations and assumptions

The tool does not execute a regex or recover captures. Null must already represent absence in the caller's observation format.
All declared input fields are required and unexpected top-level fields are rejected. Numbers must be finite; lists are limited to 128 entries and ordinary text fields to 8,192 UTF-16 code units, with tighter limits where stated.
JSON text inputs must parse within bounded nesting and size limits. Numeric outputs outside the safe finite range are rejected; large exact integer results use decimal strings. Indexes and half-open spans are zero-based unless a rank is explicitly described as one-based.

Alternative or Complementary methods

Compile generated pattern sources with explicitly chosen flags and test them on bounded representative text. Pattern sources, replacement strings and JSON string spellings require different escaping conventions.

References

Tool behavior and example: Regex Match Group Presence Table — tool.io

Similar or alternative tools

Regex Zero Width Match Budget
Budget possible zero-width progression positions from explicit UTF-16 length and code-point widths; not an actual pattern match count.
Regex Capture Index Map
Map ECMAScript capture indexes, names and opening-parenthesis UTF-16 positions after runtime syntax validation; escaped/class parentheses are ignored.