[
https://issues.apache.org/jira/browse/ARROW-2172?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16370558#comment-16370558
]
ASF GitHub Bot commented on ARROW-2172:
---------------------------------------
xhochy closed pull request #1628: ARROW-2172: [C++/Python] Fix converting from
Numpy array with non-natural stride
URL: https://github.com/apache/arrow/pull/1628
This is a PR merged from a forked repository.
As GitHub hides the original diff on merge, it is displayed below for
the sake of provenance:
As this is a foreign pull request (from a fork), the diff is supplied
below (as it won't show otherwise due to GitHub magic):
diff --git a/cpp/src/arrow/python/numpy_to_arrow.cc
b/cpp/src/arrow/python/numpy_to_arrow.cc
index 522bf5174..23418ad92 100644
--- a/cpp/src/arrow/python/numpy_to_arrow.cc
+++ b/cpp/src/arrow/python/numpy_to_arrow.cc
@@ -554,12 +554,22 @@ Status StaticCastBuffer(const Buffer& input, const
int64_t length, MemoryPool* p
return Status::OK();
}
-template <typename T, typename T2>
-void CopyStrided(T* input_data, int64_t length, int64_t stride, T2*
output_data) {
+template <typename T>
+void CopyStridedBytewise(int8_t* input_data, int64_t length, int64_t stride,
+ T* output_data) {
+ // Passing input_data as non-const is a concession to PyObject*
+ for (int64_t i = 0; i < length; ++i) {
+ memcpy(output_data + i, input_data, sizeof(T));
+ input_data += stride;
+ }
+}
+
+template <typename T>
+void CopyStridedNatural(T* input_data, int64_t length, int64_t stride, T*
output_data) {
// Passing input_data as non-const is a concession to PyObject*
int64_t j = 0;
for (int64_t i = 0; i < length; ++i) {
- output_data[i] = static_cast<T2>(input_data[j]);
+ output_data[i] = input_data[j];
j += stride;
}
}
@@ -571,13 +581,19 @@ Status CopyStridedArray(PyArrayObject* arr, const int64_t
length, MemoryPool* po
using T = typename traits::T;
// Strided, must copy into new contiguous memory
- const int64_t stride = PyArray_STRIDES(arr)[0];
- const int64_t stride_elements = stride / sizeof(T);
-
auto new_buffer = std::make_shared<PoolBuffer>(pool);
RETURN_NOT_OK(new_buffer->Resize(sizeof(T) * length));
- CopyStrided(reinterpret_cast<T*>(PyArray_DATA(arr)), length, stride_elements,
- reinterpret_cast<T*>(new_buffer->mutable_data()));
+
+ const int64_t stride = PyArray_STRIDES(arr)[0];
+ if (stride % sizeof(T) == 0) {
+ const int64_t stride_elements = stride / sizeof(T);
+ CopyStridedNatural(reinterpret_cast<T*>(PyArray_DATA(arr)), length,
stride_elements,
+ reinterpret_cast<T*>(new_buffer->mutable_data()));
+ } else {
+ CopyStridedBytewise(reinterpret_cast<int8_t*>(PyArray_DATA(arr)), length,
stride,
+ reinterpret_cast<T*>(new_buffer->mutable_data()));
+ }
+
*out = new_buffer;
return Status::OK();
}
diff --git a/python/pyarrow/tests/test_convert_pandas.py
b/python/pyarrow/tests/test_convert_pandas.py
index 95137ffb2..9bd3c77d2 100644
--- a/python/pyarrow/tests/test_convert_pandas.py
+++ b/python/pyarrow/tests/test_convert_pandas.py
@@ -1582,6 +1582,19 @@ def test_convert_empty_table(self):
arr = pa.array([], type=pa.struct([pa.field('a', pa.int64())]))
tm.assert_almost_equal(arr.to_pandas(), np.array([], dtype=object))
+ def test_non_natural_stride(self):
+ """
+ ARROW-2172: converting from a Numpy array with a stride that's
+ not a multiple of itemsize.
+ """
+ dtype = np.dtype([('x', np.int32), ('y', np.int16)])
+ data = np.array([(42, -1), (-43, 2)], dtype=dtype)
+ assert data.strides == (6,)
+ arr = pa.array(data['x'], type=pa.int32())
+ assert arr.to_pylist() == [42, -43]
+ arr = pa.array(data['y'], type=pa.int16())
+ assert arr.to_pylist() == [-1, 2]
+
def _fully_loaded_dataframe_example():
from distutils.version import LooseVersion
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> [Python] Incorrect conversion from Numpy array when stride % itemsize != 0
> --------------------------------------------------------------------------
>
> Key: ARROW-2172
> URL: https://issues.apache.org/jira/browse/ARROW-2172
> Project: Apache Arrow
> Issue Type: Bug
> Components: Python
> Affects Versions: 0.8.0
> Reporter: Antoine Pitrou
> Priority: Major
> Labels: pull-request-available
> Fix For: 0.9.0
>
>
> In the example below, the input array has a stride that's not a multiple of
> the itemsize:
> {code:python}
> >>> data = np.array([(42, True), (43, False)],
> ...: dtype=[('x', np.int32), ('y', np.bool_)])
> ...:
> ...:
> >>> data['x']
> array([42, 43], dtype=int32)
> >>> pa.array(data['x'], type=pa.int32())
> <pyarrow.lib.Int32Array object at 0x7ff60a8415e8>
> [
> 42,
> 11009
> ]
> {code}
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