ARROW-14495: [Python] Fix DictionaryArray.from_buffers, should not crash

python/pyarrow/array.pxi

@@ -2478,6 +2478,53 @@ cdef class DictionaryArray(Array):
 
         return self._indices
 
+    @staticmethod
+    def from_buffers(DataType type, int64_t length, buffers, Array dictionary,
+                     int64_t null_count=-1, int64_t offset=0):
+        """
+        Construct a DictionaryArray from buffers.
+
+        Parameters
+        ----------
+        type : pyarrow.DataType
+        length : int
+            The number of values in the array.
+        buffers : List[Buffer]
+            The buffers backing the indices array.
+        dictionary : pyarrow.Array, ndarray or pandas.Series
+            The array of values referenced by the indices.
+        null_count : int, default -1
+            The number of null entries in the indices array. Negative value means that
+            the null count is not known.
+        offset : int, default 0
+            The array's logical offset (in values, not in bytes) from the
+            start of each buffer.
+
+        Returns
+        -------
+        dict_array : DictionaryArray
+        """
+        cdef:
+            vector[shared_ptr[CBuffer]] c_buffers
+            shared_ptr[CDataType] c_type
+            shared_ptr[CArrayData] c_data
+            shared_ptr[CArray] c_result
+
+        for buf in buffers:
+            c_buffers.push_back(pyarrow_unwrap_buffer(buf))
+
+        c_type = pyarrow_unwrap_data_type(type)
+
+        with nogil:
+            c_data = CArrayData.Make(
+                c_type, length, c_buffers, null_count, offset)
+            c_data.get().dictionary = dictionary.sp_array.get().data()
+            c_result.reset(new CDictionaryArray(c_data))
+
+        cdef Array result = pyarrow_wrap_array(c_result)
+        result.validate()
+        return result
+
     @staticmethod
     def from_arrays(indices, dictionary, mask=None, bint ordered=False,
                     bint from_pandas=False, bint safe=True,

python/pyarrow/includes/libarrow.pxd

@@ -250,6 +250,7 @@ cdef extern from "arrow/api.h" namespace "arrow" nogil:
         CDictionaryArray(const shared_ptr[CDataType]& type,
                          const shared_ptr[CArray]& indices,
                          const shared_ptr[CArray]& dictionary)
+        CDictionaryArray(const shared_ptr[CArrayData]& data)
 
         @staticmethod
         CResult[shared_ptr[CArray]] FromArrays(

python/pyarrow/tests/test_array.py

@@ -725,6 +725,15 @@ def test_struct_array_from_chunked():
         pa.StructArray.from_arrays([chunked_arr], ["foo"])
 
 
+@pytest.mark.parametrize("offset", (0, 1))
+def test_dictionary_from_buffers(offset):
+    a = pa.array(["one", "two", "three", "two", "one"]).dictionary_encode()
+    b = pa.DictionaryArray.from_buffers(a.type, len(a)-offset,
+                                        a.indices.buffers(), a.dictionary,
+                                        offset=offset)
+    assert a[offset:] == b
+
+
 def test_dictionary_from_numpy():
     indices = np.repeat([0, 1, 2], 2)
     dictionary = np.array(['foo', 'bar', 'baz'], dtype=object)