ARROW-1706: [Python] Coerce array inputs to StructArray.from_arrays. Flip order of arguments

python/pyarrow/array.pxi

@@ -828,8 +828,23 @@ cdef class DictionaryArray(Array):
 
 
 cdef class StructArray(Array):
+
     @staticmethod
-    def from_arrays(field_names, arrays):
+    def from_arrays(arrays, names=None):
+        """
+        Construct StructArray from collection of arrays representing each field
+        in the struct
+
+        Parameters
+        ----------
+        arrays : sequence of Array
+        names : List[str]
+            Field names
+
+        Returns
+        -------
+        result : StructArray
+        """
         cdef:
             Array array
             shared_ptr[CArray] c_array
@@ -839,6 +854,11 @@ cdef class StructArray(Array):
             ssize_t length
             ssize_t i
 
+        if names is None:
+            raise ValueError('Names are currently required')
+
+        arrays = [asarray(x) for x in arrays]
+
         num_arrays = len(arrays)
         if num_arrays == 0:
             raise ValueError("arrays list is empty")
@@ -855,7 +875,7 @@ cdef class StructArray(Array):
         cdef DataType struct_type = struct([
             field(name, array.type)
             for name, array in
-            zip(field_names, arrays)
+            zip(names, arrays)
         ])
 
         c_result.reset(new CStructArray(struct_type.sp_type, length, c_arrays))

python/pyarrow/tests/test_convert_builtin.py

@@ -493,8 +493,8 @@ def test_structarray():
     strs = pa.array([u'a', None, u'c'], type=pa.string())
     bools = pa.array([True, False, None], type=pa.bool_())
     arr = pa.StructArray.from_arrays(
-        ['ints', 'strs', 'bools'],
-        [ints, strs, bools])
+        [ints, strs, bools],
+        ['ints', 'strs', 'bools'])
 
     expected = [
         {'ints': None, 'strs': u'a', 'bools': True},
@@ -529,3 +529,27 @@ def test_struct_from_dicts():
                 {'a': None, 'b': None, 'c': None},
                 {'a': None, 'b': 'bar', 'c': None}]
     assert arr.to_pylist() == expected
+
+
+def test_structarray_from_arrays_coerce():
+    # ARROW-1706
+    ints = [None, 2, 3]
+    strs = [u'a', None, u'c']
+    bools = [True, False, None]
+    ints_nonnull = [1, 2, 3]
+
+    arrays = [ints, strs, bools, ints_nonnull]
+    result = pa.StructArray.from_arrays(arrays,
+                                        ['ints', 'strs', 'bools',
+                                         'int_nonnull'])
+    expected = pa.StructArray.from_arrays(
+        [pa.array(ints, type='int64'),
+         pa.array(strs, type='utf8'),
+         pa.array(bools),
+         pa.array(ints_nonnull, type='int64')],
+        ['ints', 'strs', 'bools', 'int_nonnull'])
+
+    with pytest.raises(ValueError):
+        pa.StructArray.from_arrays(arrays)
+
+    assert result.equals(expected)

python/pyarrow/tests/test_convert_pandas.py

@@ -1153,8 +1153,8 @@ def test_structarray(self):
         strs = pa.array([u'a', None, u'c'], type=pa.string())
         bools = pa.array([True, False, None], type=pa.bool_())
         arr = pa.StructArray.from_arrays(
-            ['ints', 'strs', 'bools'],
-            [ints, strs, bools])
+            [ints, strs, bools],
+            ['ints', 'strs', 'bools'])
 
         expected = pd.Series([
             {'ints': None, 'strs': u'a', 'bools': True},