Join

Transform Elastic Compatible

Synopsis

Combines elements from an array into a single string using a specified separator.

Schema

join:
  - field: <ident>
  - separator: <string>
  - description: <text>
  - if: <script>
  - ignore_failure: <boolean>
  - ignore_missing: <boolean>
  - on_failure: <processor[]>
  - on_success: <processor[]>
  - tag: <string>
  - target_field: <ident>

Configuration

Field	Required	Default	Description
field	Y	-	Source field containing array of strings
separator	Y	-	String to insert between elements
description	N	-	Documentation note
if	N	-	Conditional expression
ignore_failure	N	false	Skip processing errors
ignore_missing	N	false	Skip if input field missing
on_failure	N	-	Error handling processors
on_success	N	-	Success handling processors
tag	N	-	Identifier for logging
target_field	N	field	Output field for joined string

Details

The processor expects an array of strings as input and produces a concatenated string with the specified separator between elements.

warning

Empty arrays return an empty string.

Common uses are converting arrays into human-readable lists, combining path or URL segments with appropriate separators, concatenating multiple tags, creating comma-separated values from arrays.

Missing fields can be handled with the ignore_missing flag.

Examples

Basic

Joining array elements with a comma...	{ "fruits": ["apple", "banana", "cherry"] } join: - field: fruits - separator: ", " - target_field: result
creates a comma-separated string:	{ "fruits": ["apple", "banana", "cherry"], "result": "apple, banana, cherry" }

Empty Arrays

Joining an empty array...	{ "tags": [] } join: - field: tags - separator: ";" - target_field: tag_string
creates an empty string:	{ "tags": [], "tag_string": "" }

Separator

Joining with a slash...	{ "paths": ["/home", "user", "documents"] } join: - field: paths - separator: "/" - target_field: full_path
creates a path string:	{ "paths": ["/home", "user", "documents"], "full_path": "/home/user/documents" }

Error Handling

Handling missing source field...	{ "other_field": "value" } join: - field: missing_field - separator: ", " - ignore_missing: true - on_failure: - set: - field: status - value: "field_missing"
continues execution:	{ "other_field": "value", "status": "field_missing" }