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Join processor

Joins each element of an array into a single string using a separator character between each element. Throws an error when the field is not an array.

Table 26. Join Options

Name	Required	Default	Description
`field`	yes	-	Field containing array values to join
`separator`	yes	-	The separator character
`target_field`	no	`field`	The field to assign the joined value to, by default `field` is updated in-place
`description`	no	-	Description of the processor. Useful for describing the purpose of the processor or its configuration.
`if`	no	-	Conditionally execute the processor. See Conditionally run a processor.
`ignore_failure`	no	`false`	Ignore failures for the processor. See Handling pipeline failures.
`on_failure`	no	-	Handle failures for the processor. See Handling pipeline failures.
`tag`	no	-	Identifier for the processor. Useful for debugging and metrics.

{
  "join": {
    "field": "joined_array_field",
    "separator": "-"
  }
}

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https://www.elastic.co/guide/en/elasticsearch/reference/7.17/join-processor.html