Substitute changing to float64 dtype using map with base functionalit…

…y that's accessible across Pandas versions

pvlib/tests/test_singlediode.py

@@ -110,12 +110,11 @@ def build_precise_iv_curve_dataframe(file_csv, file_json):
 
     # parse strings to np.float64
     is_array = ['Currents', 'Voltages', 'diode_voltage']
-    joined[is_array] = joined[is_array].map(
-        lambda a: np.asarray(a, dtype=np.float64)
-    )
+    for col in is_array:
+        joined[col] = [np.asarray(a, dtype=np.float64) for a in joined[col]]
     is_number = ['v_oc', 'i_sc', 'v_mp', 'i_mp', 'p_mp', 'i_x', 'i_xx',
                  'Temperature']
-    joined[is_number] = joined[is_number].map(np.float64)
+    joined[is_number] = joined[is_number].astype(np.float64)
 
     joined['Boltzmann'] = scipy.constants.Boltzmann
     joined['Elementary Charge'] = scipy.constants.elementary_charge