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tm_matchkeys Function ​

tm_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.

hcl
tm_matchkeys(valueslist, keyslist, searchset)

tm_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 ​

sh
tm_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:

sh
> [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:

sh
> [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:

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

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