From a list of maps, retrieve the values of the same key from each object as a list

@yetanotherbug wrote:

This occurs with the AWS provider, but it is a basic aspect of HCL data wrangling. Using Terraform v0.12.24.

I have a data source defined as follows that gives me a map of maps:

# Import CFN stack exports external to Terraform (not my choice, decreed by the admins)
variable "aws_private_subnets" {
  default = [
    "PrivateSubnet1",
    "PrivateSubnet2",
    "PrivateSubnet3"
  ]
}

data "aws_cloudformation_export" "private_subnets" {
  for_each = toset(var.aws_private_subnets)
  name = each.value
}

The data.aws_cloudformation_export.private_subnets has the following structure:

{
  "PrivateSubnet1" = {
    "exporting_stack_id" = "masked"
    "id" = "b"
    "name" = "PrivateSubnet1"
    "value" = "subnet-x"
  }
  "PrivateSubnet2" = {
    "exporting_stack_id" = "masked"
    "id" = "masked"
    "name" = "PrivateSubnet2"
    "value" = "subnet-y"
  }
  "PrivateSubnet3" = {
    "exporting_stack_id" = "masked"
    "id" = "masked"
    "name" = "PrivateSubnet3"
    "value" = "subnet-z"
  }
}

I wish to transform this during usage into a list of the values of the same key of each map:
["subnet-x","subnet-y","subnet-z"], that is the values of the “value” key of each object.

I can cast this map to a list by calling values() to arrive at a list of maps, but I fail to discern the correct way to collect the values. Is there an elegant way to do this basic mapping? The following and variations of it are all invalid:

data.aws_cloudformation_export.private_subnets[*].value

data.aws_cloudformation_export.private_subnets.*.value

Am I somehow implementing worst pratices by organizing data as a map of maps? Is Terraform/HCL not well equipped to wrangle nested data structures?

Thanks in advance.

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