Filtering Data in Ansible: selectattr and map(attribute)

Learn how to filter a list of dictionaries in Ansible using selectattr and map(attribute) to extract specific values efficiently.

🎯 Filtering Data in Ansible: `selectattr` and `map(attribute)`

When working with lists of dictionaries in Ansible, filtering and extracting specific values is a common requirement. Jinja2 provides two powerful filters to accomplish this:

selectattr → Filters the list based on a condition.

map(attribute) → Extracts a specific field from the filtered result.

In this article, you'll learn:

✅ How to filter lists of dictionaries in Ansible using selectattr

✅ How to extract specific values using map(attribute)

✅ How to handle missing values safely using default()

---

📌 Understanding `selectattr` and `map(attribute)`

Before jumping into Ansible playbooks, let's break down these Jinja2 filters.

✅ `selectattr('name', 'equalto', search_name')`

Filters a list of dictionaries to select only the ones where name == search_name.

✅ `map(attribute='folder')`

Extracts the folder field from the filtered result.

✅ Example Syntax

``yaml


{{ variable | selectattr('name', 'equalto', search_name) | map(attribute='folder') | list }}

selectattr filters the list where name equals search_name.

map(attribute='folder') extracts only the folder values.

list ensures the result is returned as a list.



---

🔥 Example Use Case
Scenario

You have a list of users and their home directories (folder). You want to search for a specific user and get their folder path.



Example Data

`yaml


variable:
  - name: alice
    folder: /home/alice
  - name: bob
    folder: /home/bob
  - name: charlie
    folder: /home/charlie

`Using` selectattr `and` map(attribute) `in Ansible`

`yaml


name: Search for a name and get its folder
  hosts: localhost
  gather_facts: no
  vars:
    variable:
      - name: alice
        folder: /home/alice
      - name: bob
        folder: /home/bob
      - name: charlie
        folder: /home/charlie
    search_name: alice
  tasks:
    - name: Get folder for a specific user
      debug:
        msg: "{{ variable | selectattr('name', 'equalto', search_name) | map(attribute='folder') | list }}"



---

🎯 Expected Output

When search_name: alice, the output will be:

`yaml


TASK [Get folder for a specific user] *
ok: [localhost] => {
    "msg": [
        "/home/alice"
    ]
}

When search_name: bob, the output will be:

`yaml


TASK [Get folder for a specific user] *
ok: [localhost] => {
    "msg": [
        "/home/bob"
    ]
}



---

🔹 Getting a Single Value Instead of a List

By default, the output is a list with one value. If you need only the string value, add .0:

`yaml


name: Get a single folder for a user
  debug:
    msg: "{{ (variable | selectattr('name', 'equalto', search_name) | map(attribute='folder') | list).0 }}"



📌 Expected Output

``yaml

TASK

Filtering Data in Ansible: selectattr and map(attribute)