[BEAM-7390] Add code snippet for Latest (#10166)

[BEAM-7390] Add code snippet for Latest (#10166)

sdks/python/apache_beam/examples/snippets/transforms/aggregation/latest.py

@@ -0,0 +1,84 @@
+# coding=utf-8
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+from __future__ import absolute_import
+from __future__ import print_function
+
+
+def latest_globally(test=None):
+  # [START latest_globally]
+  import apache_beam as beam
+  import time
+
+  def to_unix_time(time_str, format='%Y-%m-%d %H:%M:%S'):
+    return time.mktime(time.strptime(time_str, format))
+
+  with beam.Pipeline() as pipeline:
+    latest_element = (
+        pipeline
+        | 'Create crops' >> beam.Create([
+            {'item': '🥬', 'harvest': '2020-02-24 00:00:00'},
+            {'item': '🍓', 'harvest': '2020-06-16 00:00:00'},
+            {'item': '🥕', 'harvest': '2020-07-17 00:00:00'},
+            {'item': '🍆', 'harvest': '2020-10-26 00:00:00'},
+            {'item': '🍅', 'harvest': '2020-10-01 00:00:00'},
+        ])
+        | 'With timestamps' >> beam.Map(
+            lambda crop: beam.window.TimestampedValue(
+                crop['item'], to_unix_time(crop['harvest'])))
+        | 'Get latest element' >> beam.combiners.Latest.Globally()
+        | beam.Map(print)
+    )
+    # [END latest_globally]
+    if test:
+      test(latest_element)
+
+
+def latest_per_key(test=None):
+  # [START latest_per_key]
+  import apache_beam as beam
+  import time
+
+  def to_unix_time(time_str, format='%Y-%m-%d %H:%M:%S'):
+    return time.mktime(time.strptime(time_str, format))
+
+  with beam.Pipeline() as pipeline:
+    latest_elements_per_key = (
+        pipeline
+        | 'Create crops' >> beam.Create([
+            ('spring', {'item': '🥕', 'harvest': '2020-06-28 00:00:00'}),
+            ('spring', {'item': '🍓', 'harvest': '2020-06-16 00:00:00'}),
+            ('summer', {'item': '🥕', 'harvest': '2020-07-17 00:00:00'}),
+            ('summer', {'item': '🍓', 'harvest': '2020-08-26 00:00:00'}),
+            ('summer', {'item': '🍆', 'harvest': '2020-09-04 00:00:00'}),
+            ('summer', {'item': '🥬', 'harvest': '2020-09-18 00:00:00'}),
+            ('summer', {'item': '🍅', 'harvest': '2020-09-22 00:00:00'}),
+            ('autumn', {'item': '🍅', 'harvest': '2020-10-01 00:00:00'}),
+            ('autumn', {'item': '🥬', 'harvest': '2020-10-20 00:00:00'}),
+            ('autumn', {'item': '🍆', 'harvest': '2020-10-26 00:00:00'}),
+            ('winter', {'item': '🥬', 'harvest': '2020-02-24 00:00:00'}),
+        ])
+        | 'With timestamps' >> beam.Map(
+            lambda pair: beam.window.TimestampedValue(
+                (pair[0], pair[1]['item']), to_unix_time(pair[1]['harvest'])))
+        | 'Get latest elements per key' >> beam.combiners.Latest.PerKey()
+        | beam.Map(print)
+    )
+    # [END latest_per_key]
+    if test:
+      test(latest_elements_per_key)

sdks/python/apache_beam/examples/snippets/transforms/aggregation/latest_test.py

@@ -0,0 +1,61 @@
+# coding=utf-8
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+from __future__ import absolute_import
+from __future__ import print_function
+
+import unittest
+
+import mock
+
+from apache_beam.examples.snippets.util import assert_matches_stdout
+from apache_beam.testing.test_pipeline import TestPipeline
+
+from . import latest
+
+
+def check_latest_element(actual):
+  expected = '''[START latest_element]
+🍆
+[END latest_element]'''.splitlines()[1:-1]
+  assert_matches_stdout(actual, expected)
+
+
+def check_latest_elements_per_key(actual):
+  expected = '''[START latest_elements_per_key]
+('spring', '🥕')
+('summer', '🍅')
+('autumn', '🍆')
+('winter', '🥬')
+[END latest_elements_per_key]'''.splitlines()[1:-1]
+  assert_matches_stdout(actual, expected)
+
+
+@mock.patch('apache_beam.Pipeline', TestPipeline)
+@mock.patch(
+    'apache_beam.examples.snippets.transforms.aggregation.latest.print', str)
+class LatestTest(unittest.TestCase):
+  def test_latest_globally(self):
+    latest.latest_globally(check_latest_element)
+
+  def test_latest_per_key(self):
+    latest.latest_per_key(check_latest_elements_per_key)
+
+
+if __name__ == '__main__':
+  unittest.main()