ENH: Allow genfromtxt to unpack structured arrays (#16650)

* ENH: Allow genfromtxt to unpack structured arrays

genfromtxt failed to transpose output when
unpack=True and `dtype` was structured (or None).
This patch resolves the issue by
returning a list of arrays, as in `loadtxt`.

Co-authored-by: Matti Picus <matti.picus@gmail.com>
Co-authored-by: Eric Wieser <wieser.eric@gmail.com>
Co-authored-by: Sebastian Berg <sebastian@sipsolutions.net>
Co-authored-by: Ross Barnowski <rossbar@berkeley.edu>

1 files changed, 46 insertions, 1 deletions

diff --git a/numpy/lib/tests/test_io.py b/numpy/lib/tests/test_io.py
index 38d698df4..aa4499764 100644
--- a/numpy/lib/tests/test_io.py
+++ b/numpy/lib/tests/test_io.py
@@ -1026,7 +1026,7 @@ class TestLoadTxt(LoadTxtBase):
         a = np.array([b'start ', b'  ', b''])
         assert_array_equal(x['comment'], a)
 
-    def test_structure_unpack(self):
+    def test_unpack_structured(self):
         txt = TextIO("M 21 72\nF 35 58")
         dt = {'names': ('a', 'b', 'c'), 'formats': ('|S1', '<i4', '<f4')}
         a, b, c = np.loadtxt(txt, dtype=dt, unpack=True)
@@ -2358,6 +2358,51 @@ M   33  21.99
         assert_equal(test['f1'], 17179869184)
         assert_equal(test['f2'], 1024)
 
+    def test_unpack_structured(self):
+        # Regression test for gh-4341
+        # Unpacking should work on structured arrays
+        txt = TextIO("M 21 72\nF 35 58")
+        dt = {'names': ('a', 'b', 'c'), 'formats': ('S1', 'i4', 'f4')}
+        a, b, c = np.genfromtxt(txt, dtype=dt, unpack=True)
+        assert_equal(a.dtype, np.dtype('S1'))
+        assert_equal(b.dtype, np.dtype('i4'))
+        assert_equal(c.dtype, np.dtype('f4'))
+        assert_array_equal(a, np.array([b'M', b'F']))
+        assert_array_equal(b, np.array([21, 35]))
+        assert_array_equal(c, np.array([72.,  58.]))
+
+    def test_unpack_auto_dtype(self):
+        # Regression test for gh-4341
+        # Unpacking should work when dtype=None
+        txt = TextIO("M 21 72.\nF 35 58.")
+        expected = (np.array(["M", "F"]), np.array([21, 35]), np.array([72., 58.]))
+        test = np.genfromtxt(txt, dtype=None, unpack=True, encoding="utf-8")
+        for arr, result in zip(expected, test):
+            assert_array_equal(arr, result)
+            assert_equal(arr.dtype, result.dtype)
+
+    def test_unpack_single_name(self):
+        # Regression test for gh-4341
+        # Unpacking should work when structured dtype has only one field
+        txt = TextIO("21\n35")
+        dt = {'names': ('a',), 'formats': ('i4',)}
+        expected = np.array([21, 35], dtype=np.int32)
+        test = np.genfromtxt(txt, dtype=dt, unpack=True)
+        assert_array_equal(expected, test)
+        assert_equal(expected.dtype, test.dtype)
+
+    def test_squeeze_scalar(self):
+        # Regression test for gh-4341
+        # Unpacking a scalar should give zero-dim output,
+        # even if dtype is structured
+        txt = TextIO("1")
+        dt = {'names': ('a',), 'formats': ('i4',)}
+        expected = np.array((1,), dtype=np.int32)
+        test = np.genfromtxt(txt, dtype=dt, unpack=True)
+        assert_array_equal(expected, test)
+        assert_equal((), test.shape)
+        assert_equal(expected.dtype, test.dtype)
+
 
 class TestPathUsage:
     # Test that pathlib.Path can be used