refactor gluon.utils.split_data() following np.array_split() (#17123)

* fix

* fix & add test

* add mx.numpy test

* fix name

* fix mis input

* fix test

Author: zburning

python/mxnet/gluon/utils.py

@@ -70,30 +70,18 @@ def split_data(data, num_slice, batch_axis=0, even_split=True):
             "uneven partitioning of data."%(
                 str(data.shape), num_slice, batch_axis, num_slice))
 
-    step = size // num_slice
-
-    # If size < num_slice, make fewer slices
-    if not even_split and size < num_slice:
-        step = 1
-        num_slice = size
-
-    if batch_axis == 0:
-        slices = [data[i*step:(i+1)*step] if i < num_slice - 1 else data[i*step:size]
-                  for i in range(num_slice)]
-    elif even_split:
-        if is_np_array():
-            slices = _mx_np.split(data, indices_or_sections=num_slice, axis=batch_axis)
-        else:
-            slices = ndarray.split(data, num_outputs=num_slice, axis=batch_axis)
+    n_each_section, extras = divmod(size, num_slice)
+    section_sizes = [0] + (extras * [n_each_section + 1] +
+                           (num_slice - extras) * [n_each_section])
+    div_points = np.array(section_sizes).cumsum()
+    if is_np_array():
+        slices = _mx_np.split(data, indices_or_sections=list(div_points[1: -1]), axis=batch_axis)
     else:
-        if is_np_array():
-            indices = [step * i for i in range(1, num_slice)]
-            slices = _mx_np.split(data, indices_or_sections=indices, axis=batch_axis)
-        else:
-            slices = [ndarray.slice_axis(data, batch_axis, i*step, (i+1)*step)
-                      if i < num_slice - 1 else
-                      ndarray.slice_axis(data, batch_axis, i*step, size)
-                      for i in range(num_slice)]
+        slices = []
+        for i in range(num_slice):
+            st = div_points[i]
+            end = div_points[i + 1]
+            slices.append(ndarray.slice_axis(data, axis=batch_axis, begin=st, end=end))
     return slices
 
 

tests/python/unittest/test_gluon.py

@@ -23,7 +23,10 @@
 from mxnet.gluon import nn
 from mxnet.base import py_str
 from mxnet.test_utils import assert_almost_equal
+from mxnet.util import is_np_array
 from mxnet.ndarray.ndarray import _STORAGE_TYPE_STR_TO_ID
+from mxnet.test_utils import use_np
+import mxnet.numpy as _mx_np
 from common import (setup_module, with_seed, assertRaises, teardown,
                     assert_raises_cudnn_not_satisfied)
 import numpy as np
@@ -952,17 +955,39 @@ def test_deferred_init():
     layer(x)
 
 
+
 def check_split_data(x, num_slice, batch_axis, **kwargs):
     res = gluon.utils.split_data(x, num_slice, batch_axis, **kwargs)
     assert len(res) == num_slice
-    mx.test_utils.assert_almost_equal(mx.nd.concat(*res, dim=batch_axis).asnumpy(),
-                                      x.asnumpy())
+    if not is_np_array():
+        mx.test_utils.assert_almost_equal(mx.nd.concat(*res, dim=batch_axis).asnumpy(),
+                                          x.asnumpy())
+    else:
+        mx.test_utils.assert_almost_equal(_mx_np.concatenate(res, axis=batch_axis).asnumpy(),
+                                          x.asnumpy())
+    np_res = np.array_split(x.asnumpy(), num_slice, axis=batch_axis)
+    res_asnp = [s.asnumpy() for s in res]
+    for r1, r2 in zip(np_res, res_asnp):
+        assert all(r1.reshape(-1) == r2.reshape(-1))
 
 
+@with_seed()
+@use_np
+def test_split_data_np():
+    x = _mx_np.random.uniform(size=(128, 33, 64))
+    check_split_data(x, 8, 0)
+    check_split_data(x, 3, 1)
+    check_split_data(x, 4, 1, even_split=False)
+    check_split_data(x, 15, 1, even_split=False)
+    try:
+        check_split_data(x, 4, 1)
+    except ValueError:
+        return
+    assert False, "Should have failed"
+
 @with_seed()
 def test_split_data():
     x = mx.nd.random.uniform(shape=(128, 33, 64))
-
     check_split_data(x, 8, 0)
     check_split_data(x, 3, 1)
     check_split_data(x, 4, 1, even_split=False)
@@ -973,7 +998,6 @@ def test_split_data():
         return
     assert False, "Should have failed"
 
-
 @with_seed()
 def test_flatten():
     flatten = nn.Flatten()