move interval sampler to contrib

python/mxnet/gluon/contrib/data/__init__.py

@@ -20,3 +20,5 @@
 """Contrib datasets."""
 
 from . import text
+
+from .sampler import *

python/mxnet/gluon/contrib/data/sampler.py

@@ -0,0 +1,62 @@
+# 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.
+
+# coding: utf-8
+# pylint: disable=
+"""Dataset sampler."""
+__all__ = ['IntervalSampler']
+
+from ...data import sampler
+
+class IntervalSampler(sampler.Sampler):
+    """Samples elements from [0, length) at fixed intervals.
+
+    Parameters
+    ----------
+    length : int
+        Length of the sequence.
+    interval : int
+        The number of items to skip between two samples.
+    rollover : bool, default True
+        Whether to start again from the first skipped item after reaching the end.
+        If true, this sampler would start again from the first skipped item until all items
+        are visited.
+        Otherwise, iteration stops when end is reached and skipped items are ignored.
+
+    Examples
+    --------
+    >>> sampler = contrib.data.IntervalSampler(13, interval=3)
+    >>> list(sampler)
+    [0, 3, 6, 9, 12, 1, 4, 7, 10, 2, 5, 8, 11]
+    >>> sampler = contrib.data.IntervalSampler(13, interval=3, rollover=False)
+    >>> list(sampler)
+    [0, 3, 6, 9, 12]
+    """
+    def __init__(self, length, interval, rollover=True):
+        assert interval < length, \
+            "Interval {} must be smaller than length {}".format(interval, length)
+        self._length = length
+        self._interval = interval
+        self._rollover = rollover
+
+    def __iter__(self):
+        for i in range(self._interval if self._rollover else 1):
+            for j in range(i, self._length, self._interval):
+                yield j
+
+    def __len__(self):
+        return self._length

tests/python/unittest/test_gluon_contrib.py

@@ -178,6 +178,13 @@ def test_datasets():
     assert len(contrib.data.text.WikiText2(root='data/wikitext-2', segment='test')) == 15941
 
 
+def test_sampler():
+    interval_sampler = contrib.data.IntervalSampler(10, 3)
+    assert sorted(list(interval_sampler)) == list(range(10))
+    interval_sampler = contrib.data.IntervalSampler(10, 3, rollover=False)
+    assert list(interval_sampler) == [0, 3, 6, 9]
+
+
 if __name__ == '__main__':
     import nose
     nose.runmodule()