Prevent empty data from being coerced to float64

Author: Pyry Kovanen

pandas/io/json/json.py

@@ -658,6 +658,7 @@ def _try_convert_types(self):
 
     def _try_convert_data(self, name, data, use_dtypes=True,
                           convert_dates=True):
+        print(data)
         """ try to parse a ndarray like into a column by inferring dtype """
 
         # don't try to coerce, unless a force conversion
@@ -686,7 +687,7 @@ def _try_convert_data(self, name, data, use_dtypes=True,
 
         result = False
 
-        if data.dtype == 'object':
+        if len(data) and data.dtype == 'object':
 
             # try float
             try:

pandas/tests/io/json/test_json_table_schema.py

@@ -1,5 +1,6 @@
 """Tests for Table Schema integration."""
 import json
+import io
 from collections import OrderedDict
 
 import numpy as np
@@ -566,6 +567,6 @@ def test_empty_frame_roundtrip(self):
         # GH 21287
         df = pd.DataFrame([], columns=['a', 'b', 'c'])
         expected = df.copy()
-        out = df.to_json(None, orient='table')
+        out = df.to_json(orient='table')
         result = pd.read_json(out, orient='table')
-        pd.testing.assert_frame_equal(expected, result)
+        tm.assert_frame_equal(expected, result)