Add counter filter (#3921)

* Add counter filter

* move counter filter doc to existing chapter

* Use existing typerror exception from Counter

* Match counter filter example task name and output

plugins/filter/counter.py

@@ -0,0 +1,36 @@
+# -*- coding: utf-8 -*-
+# Copyright (c) 2021, Remy Keil <remy.keil@gmail.com>
+# 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 Sequence
+from collections import Counter
+
+
+def counter(sequence):
+    ''' Count elements in a sequence. Returns dict with count result. '''
+    if not isinstance(sequence, Sequence):
+        raise AnsibleFilterError('Argument for community.general.counter must be a sequence (string or list). %s is %s' %
+                                 (sequence, type(sequence)))
+
+    try:
+        result = dict(Counter(sequence))
+    except TypeError as e:
+        raise AnsibleFilterError(
+            "community.general.counter needs a sequence with hashable elements (int, float or str) - %s" % (e)
+        )
+    return result
+
+
+class FilterModule(object):
+    ''' Ansible counter jinja2 filters '''
+
+    def filters(self):
+        filters = {
+            'counter': counter,
+        }
+
+        return filters