Add groupby_as_dict filter (#2323) (#2503)

* Add groupby_as_dict filter.

* Test all error cases.

(cherry picked from commit 384655e15c)

Co-authored-by: Felix Fontein <felix@fontein.de>

changelogs/fragments/2323-groupby_as_dict-filter.yml

@@ -0,0 +1,3 @@
+add plugin.filter:
+  - name: groupby_as_dict
+    description: Transform a sequence of dictionaries to a dictionary where the dictionaries are indexed by an attribute

plugins/filter/groupby.py

@@ -0,0 +1,42 @@
+# -*- coding: utf-8 -*-
+# Copyright (c) 2021, Felix Fontein <felix@fontein.de>
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+from ansible.errors import AnsibleFilterError
+from ansible.module_utils.common._collections_compat import Mapping, Sequence
+
+
+def groupby_as_dict(sequence, attribute):
+    '''
+    Given a sequence of dictionaries and an attribute name, returns a dictionary mapping
+    the value of this attribute to the dictionary.
+
+    If multiple dictionaries in the sequence have the same value for this attribute,
+    the filter will fail.
+    '''
+    if not isinstance(sequence, Sequence):
+        raise AnsibleFilterError('Input is not a sequence')
+
+    result = dict()
+    for list_index, element in enumerate(sequence):
+        if not isinstance(element, Mapping):
+            raise AnsibleFilterError('Sequence element #{0} is not a mapping'.format(list_index))
+        if attribute not in element:
+            raise AnsibleFilterError('Attribute not contained in element #{0} of sequence'.format(list_index))
+        result_index = element[attribute]
+        if result_index in result:
+            raise AnsibleFilterError('Multiple sequence entries have attribute value {0!r}'.format(result_index))
+        result[result_index] = element
+    return result
+
+
+class FilterModule(object):
+    ''' Ansible list filters '''
+
+    def filters(self):
+        return {
+            'groupby_as_dict': groupby_as_dict,
+        }

tests/integration/targets/filter_groupby/aliases

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+shippable/posix/group4
+skip/python2.6  # filters are controller only, and we no longer support Python 2.6 on the controller

tests/integration/targets/filter_groupby/tasks/main.yml

@@ -0,0 +1,45 @@
+---
+- name: Test functionality
+  assert:
+    that:
+      - list1 | community.general.groupby_as_dict('name') == dict1
+
+- name: 'Test error: not a list'
+  set_fact:
+    test: "{{ list_no_list | community.general.groupby_as_dict('name') }}"
+  ignore_errors: true
+  register: result
+
+- assert:
+    that:
+      - result.msg == 'Input is not a sequence'
+
+- name: 'Test error: list element not a mapping'
+  set_fact:
+    test: "{{ list_no_dict | community.general.groupby_as_dict('name') }}"
+  ignore_errors: true
+  register: result
+
+- assert:
+    that:
+      - "result.msg == 'Sequence element #0 is not a mapping'"
+
+- name: 'Test error: list element does not have attribute'
+  set_fact:
+    test: "{{ list_no_attribute | community.general.groupby_as_dict('name') }}"
+  ignore_errors: true
+  register: result
+
+- assert:
+    that:
+      - "result.msg == 'Attribute not contained in element #1 of sequence'"
+
+- name: 'Test error: attribute collision'
+  set_fact:
+    test: "{{ list_collision | community.general.groupby_as_dict('name') }}"
+  ignore_errors: true
+  register: result
+
+- assert:
+    that:
+      - result.msg == "Multiple sequence entries have attribute value 'a'"

tests/integration/targets/filter_groupby/vars/main.yml

@@ -0,0 +1,31 @@
+---
+list1:
+  - name: a
+    x: y
+  - name: b
+    z: 1
+
+dict1:
+  a:
+    name: a
+    x: y
+  b:
+    name: b
+    z: 1
+
+list_no_list:
+  a:
+    name: a
+
+list_no_dict:
+  - []
+  - 1
+
+list_no_attribute:
+  - name: a
+    foo: baz
+  - foo: bar
+
+list_collision:
+  - name: a
+  - name: a