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

The following fields are used to define the processor:

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" }