terraform/website/docs/configuration/functions/matchkeys.html.md

layout	page_title	sidebar_current	description
functions	matchkeys - Functions - Configuration Language	docs-funcs-collection-matchkeys	The matchkeys function takes a subset of elements from one list by matching corresponding indexes in another list.

matchkeys Function

-> Note: This page is about Terraform 0.12 and later. For Terraform 0.11 and earlier, see 0.11 Configuration Language: Interpolation Syntax.

matchkeys constructs a new list by taking a subset of elements from one list whose indexes match the corresponding indexes of values in another list.

matchkeys(valueslist, keyslist, searchset)

matchkeys identifies the indexes in keyslist that are equal to elements of searchset, and then constructs a new list by taking those same indexes from valueslist. Both valueslist and keyslist must be the same length.

The ordering of the values in valueslist is preserved in the result.

Examples

> matchkeys(["i-123", "i-abc", "i-def"], ["us-west", "us-east", "us-east"], ["us-east"])
[
  "i-abc",
  "i-def",
]

If the result ordering is not significant, you can achieve a similar result using a for expression with a map:

> [for i, z in {"i-123"="us-west","i-abc"="us-east","i-def"="us-east"}: i if z == "us-east"]
[
  "i-def",
  "i-abc",
]

If the keys and values of interest are attributes of objects in a list of objects then you can also achieve a similar result using a for expression with that list:

> [for x in [{id="i-123",zone="us-west"},{id="i-abc",zone="us-east"}]: x.id if x.zone == "us-east"]
[
  "i-abc",
]

For example, the previous form can be used with the list of resource instances produced by a resource block with the count meta-attribute set, to filter the instances by matching one of the resource attributes:

> [for x in aws_instance.example: x.id if x.availability_zone == "us-east-1a"]
[
  "i-abc123",
  "i-def456",
]

Since the signature of matchkeys is complicated and not immediately clear to the reader when used in configuration, prefer to use for expressions where possible to maximize readability.