fix: reading RNTuple fields into NumPy

src/uproot/behaviors/RNTuple.py

@@ -860,7 +860,10 @@ def arrays(
                             "The array was not constructed correctly. Please report this issue."
                         )
 
-        # FIXME: This is not right, but it might temporarily work
+        # TODO: The conversion would be ideally be fully handled by Awkward.
+        # However, jagged arrays fail to be converted.
+        # We still need to match the TTree behavior for jagged arrays, and implement
+        # the conversion to Pandas.
         if library.name == "np":
             return arrays.to_numpy()
 

src/uproot/models/RNTuple.py

@@ -1876,7 +1876,7 @@ def array(
             entry_start=entry_start,
             entry_stop=entry_stop,
             array_cache=array_cache,
-            library=library,
+            library="ak",  # conversion needs to be done at the end
             interpreter=interpreter,
             backend=backend,
             ak_add_doc=ak_add_doc,
@@ -1893,6 +1893,14 @@ def array(
                 raise AssertionError(
                     "The array was not constructed correctly. Please report this issue."
                 )
+        library = uproot.interpretation.library._regularize_library(library)
+        # TODO: The conversion would be ideally be fully handled by Awkward.
+        # However, jagged arrays fail to be converted.
+        # We still need to match the TTree behavior for jagged arrays, and implement
+        # the conversion to Pandas.
+        if library.name == "np":
+            return arrays.to_numpy()
+
         return arrays
 
 

tests/test_1591_rntuple_read_to_numpy.py

@@ -0,0 +1,23 @@
+# BSD 3-Clause License; see https://github.com/scikit-hep/uproot5/blob/main/LICENSE
+
+import skhep_testdata
+import awkward as ak
+import uproot
+
+
+def test_reading_into_numpy():
+    filename = skhep_testdata.data_path(
+        "Run2012BC_DoubleMuParked_Muons_1000evts_rntuple_v1-0-0-0.root"
+    )
+    with uproot.open(filename) as f:
+        obj = f["Events"]
+        ak_arrays = obj.arrays(filter_name="n*")
+        np_arrays = obj.arrays(library="np", filter_name="n*")
+
+        nmuon_ak_array = obj["nMuon"].array()
+        nmuon_np_array = obj["nMuon"].array(library="np")
+
+        assert ak.array_equal(nmuon_ak_array, nmuon_np_array)
+        assert ak.array_equal(ak_arrays["nMuon"], np_arrays["nMuon"])
+        assert ak.array_equal(ak_arrays["nMuon"], nmuon_ak_array)
+        assert ak.array_equal(np_arrays["nMuon"], nmuon_np_array)