Remove duplicates from output - terraform

Question

I have the following output:
output "regions_data" {
value = regions({
for region, data in var.regions :
regions => "${region}/${data.postcode}"
})
}
Which contains duplicates like(it is intentional):
regions = {
reg1 = {
postcode = "1"
},
reg1 = {
postcode = "1"
},
reg2 = {
postcode = "2"
}
}
How can I remove the duplicates from the output?

Answer 1

Your code does not comply to the basic rules of maps or objects. Nor there is any regions function you use in the code. The provided code is not a proper Terraform syntax.
I believe however, you might have meant the following example:
variable "regions" {
default = {
reg1 = [
{
postcode = 1
area = "oak-county"
},
{
postcode = 2
area = "birch-county"
}
],
reg2 = [
{
postcode = 1
area = "fir-county"
},
{
postcode = 2
area = "pine-county"
}
],
}
}
In a case, when the two maps have the same keys, you can use flatten to break up everything to pieces, then rejoin everything back together:
locals {
flatten = flatten([
for region_key, region in var.regions : [
for area in region :
{
key = "${region_key}-${area.postcode}"
value = area.area
}
]
])
}
output "flattened_regions" {
value = local.flatten
}
output "remap" {
value = { for key, data in local.flatten :
data.key => data.value
}
}
Even if the code above doesn't exactly fit your case, please experiment in a similar manner - or, provide more complete example of variables you have and the outcome you need.
Source: https://www.terraform.io/language/functions/flatten

Answer 2

Probably what you want
I have no idea what you've meant by regions in value = regions({ but I assume that this code will do what you want:
locals {
regions = {
reg1 = {
postcode = "1"
},
reg1 = {
postcode = "1"
},
reg2 = {
postcode = "2"
}
}
}
output "regions_data" {
value = {
for region, data in local.regions :
region => "${region}/${data.postcode}"
}
}
Keep in mind that I replaced var with local to have one file.
And output of such is:
regions_data = {
"reg1" = "reg1/1"
"reg2" = "reg2/2"
}
Thought be warned that it will use one of keys. It doesn't check for duplicates. It just takes first one.
But why you shouldn't want it
This solution is quite bad for multiple reasons:
You provide variables - why the heck would you put duplicates? :)
As I said this merge will not necessarily provide the output you what
If var is provided by some terraform code (e.g. this regions_data is in module) then logic of merging should be done outside of module and probably terraform's own merge would be the answer.