msuzoagu · July 9, 2023 21:40 · Nov 24, 2020 · Nov 24, 2020 · Nov 24, 2020 · Nov 24, 2020
diff --git a/README.md b/README.md
@@ -27,7 +27,7 @@ BUT!!!
 
 You CAN do group_by with terraform!
 
-This is how you do a group by employee to get projects per employee:
+This is how you do a group by project to get employees of a project:
 
 ```hcl
 output project_employees {

diff --git a/README.md b/README.md
@@ -30,10 +30,10 @@ You CAN do group_by with terraform!
 This is how you do a group by employee to get projects per employee:
 
 ```hcl
-output employee_projects {
+output project_employees {
   value = {
     for item in local.input :
-    item.employee => item.project...
+    item.project => item.employee...
   }
 }
 ```

diff --git a/README.md b/README.md
@@ -27,7 +27,7 @@ BUT!!!
 
 You CAN do group_by with terraform!
 
-This is how you do a group by project:
+This is how you do a group by employee to get projects per employee:
 
 ```hcl
 output employee_projects {

diff --git a/README.md b/README.md
@@ -0,0 +1,80 @@
+# The Terraform group_by you've been missing
+
+I'm playing around a lot nowadays with Terraform 0.13 and I found a really interesting feature and that's the `...` symbol (also called an ellipsis) to be used with `for` expressions.
+
+The operator can be used for group_by operations.
+
+## Example
+
+We have a list of entries. The list contains employee/manager/project triplets.
+
+```hcl
+locals {
+  input = [
+    { employee = "Pete", manager = "Joe", project = "DEF" },
+    { employee = "Paul", manager = "Joe", project = "ABC" },
+    { employee = "Paul", manager = "Joe", project = "DEF" },
+    { employee = "Pam", manager = "Jim", project = "ABC" },
+  ]
+}
+```
+
+The goal is to group the list by either one of the attributes.
+
+First you'd try to go check terraform built-in function for group_by, but after an hour of groking the terraform documentation you realize that terraform doesn't have a built-in group-by function for a list of maps/objects. You start to give up.
+
+BUT!!!
+
+You CAN do group_by with terraform!
+
+This is how you do a group by project:
+
+```hcl
+output employee_projects {
+  value = {
+    for item in local.input :
+    item.employee => item.project...
+  }
+}
+```
+
+And given the above input, you'd get this output:
+```hcl
+{
+  "ABC" = [
+    "Paul",
+    "Pam",
+  ]
+  "DEF" = [
+    "Pete",
+    "Paul",
+  ]
+}
+```
+
+
+The crucial part is the `...`. This feature is hidden deep in the documentation of the [`for` expression](https://www.terraform.io/docs/configuration/expressions.html#for-expressions) with only a single example to grab onto:
+
+> Finally, if the result type is an object (using `{` and `}` delimiters) then the value result expression can be followed by the `...` symbol to group together results that have a common key:
+```hcl
+{for s in var.list : substr(s, 0, 1) => s... if s != ""}
+```
+
+There was also a [blog post introducing TF 0.12 `for` and `for_each`](https://www.hashicorp.com/blog/hashicorp-terraform-0-12-preview-for-and-for-each) that mentions this feature:
+
+> Finally, the map form of a `for` expression has a grouping mode where the map key is used to group items together into a list for each distinct key. This mode is activated by placing an ellipsis (`...`) after the value expression:
+```hcl
+# Configuration for Terraform 0.12
+output "instances_by_availability_zone" {
+  # Result is a map from availability zone to instance ids, such as:
+  #  {"us-east-1a": ["i-1234", "i-5678"]}
+  value = {
+    for instance in aws_instance.example:
+    instance.availability_zone => instance.id...
+  }
+}
+```
+> In the the example above we show that a resource with count set now also behaves as a list, allowing all of the instances of `aws_instance.example` to be iterated over to produce a grouping by availability zone.
+
+
+And that's how you group_by in Terraform!
diff --git a/gistfile1.txt b/gistfile1.txt
@@ -1,52 +0,0 @@
-# The Terraform group_by you've been missing
-
-I'm playing around a lot nowadays with Terraform 0.13 and I found a really interesting
-feature and that's the `...` operator for for expressions.
-
-The operator can be used for group_by operations.
-
-## Example
-
-We have a list of entries. The list contains employee/manager/project triplets.
-
-```hcl
-locals {
-  input = [
-    { employee = "Pete", manager = "Joe", project = "DEF" },
-    { employee = "Paul", manager = "Joe", project = "ABC" },
-    { employee = "Paul", manager = "Joe", project = "DEF" },
-    { employee = "Pam", manager = "Jim", project = "ABC" },
-  ]
-}
-```
-
-The goal is to group the list by either one of the attributes.
-
-First you'd try to go check terraform built-in function for group_by, but after an hour of grokking
-the terraform documentation you realize that terraform doesn't have a built-in group-by function
-for a list of maps/objects. You start to give up.
-
-BUT!!!
-
-You CAN do group_by with terraform!
-
-This is how you do a group by project:
-
-```hcl
-output employee_projects {
-  value = {
-    for item in local.input :
-    item.employee => item.project...
-  }
-}
-```
-
-The crucial part is the `...`. This feature is hidden deep in the documentation of the
-[for expression](https://www.terraform.io/docs/configuration/expressions.html#for-expressions)
-
-> Finally, if the result type is an object (using { and } delimiters) then the value result expression can be followed by the ... symbol to group together results that have a common key:
-
-{for s in var.list : substr(s, 0, 1) => s... if s != ""}
-
-
-And that's how you group_by in Terraform!

diff --git a/gistfile1.txt b/gistfile1.txt
@@ -0,0 +1,52 @@
+# The Terraform group_by you've been missing
+
+I'm playing around a lot nowadays with Terraform 0.13 and I found a really interesting
+feature and that's the `...` operator for for expressions.
+
+The operator can be used for group_by operations.
+
+## Example
+
+We have a list of entries. The list contains employee/manager/project triplets.
+
+```hcl
+locals {
+  input = [
+    { employee = "Pete", manager = "Joe", project = "DEF" },
+    { employee = "Paul", manager = "Joe", project = "ABC" },
+    { employee = "Paul", manager = "Joe", project = "DEF" },
+    { employee = "Pam", manager = "Jim", project = "ABC" },
+  ]
+}
+```
+
+The goal is to group the list by either one of the attributes.
+
+First you'd try to go check terraform built-in function for group_by, but after an hour of grokking
+the terraform documentation you realize that terraform doesn't have a built-in group-by function
+for a list of maps/objects. You start to give up.
+
+BUT!!!
+
+You CAN do group_by with terraform!
+
+This is how you do a group by project:
+
+```hcl
+output employee_projects {
+  value = {
+    for item in local.input :
+    item.employee => item.project...
+  }
+}
+```
+
+The crucial part is the `...`. This feature is hidden deep in the documentation of the
+[for expression](https://www.terraform.io/docs/configuration/expressions.html#for-expressions)
+
+> Finally, if the result type is an object (using { and } delimiters) then the value result expression can be followed by the ... symbol to group together results that have a common key:
+
+{for s in var.list : substr(s, 0, 1) => s... if s != ""}
+
+
+And that's how you group_by in Terraform!
diff --git a/main.tf b/main.tf
@@ -0,0 +1,29 @@
+locals {
+  input = [
+    { employee = "Pete", manager = "Joe", project = "DEF" },
+    { employee = "Paul", manager = "Joe", project = "ABC" },
+    { employee = "Paul", manager = "Joe", project = "DEF" },
+    { employee = "Pam", manager = "Jim", project = "ABC" },
+  ]
+}
+
+output project_employees {
+  value = {
+    for item in local.input :
+    item.project => item.employee...
+  }
+}
+
+output employee_projects {
+  value = {
+    for item in local.input :
+    item.employee => item.project...
+  }
+}
+
+output manager_employees {
+  value = {
+    for item in local.input :
+    item.manager => item.employee...
+  }
+}
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