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BUG: Fix empty Data frames to JSON round-trippable back to data frames #21318

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Merged
merged 15 commits into from
Jun 8, 2018
Merged
1 change: 1 addition & 0 deletions doc/source/whatsnew/v0.23.1.txt
Original file line number Diff line number Diff line change
Expand Up @@ -122,6 +122,7 @@ Bug Fixes
- Bug in IO methods specifying ``compression='zip'`` which produced uncompressed zip archives (:issue:`17778`, :issue:`21144`)
- Bug in :meth:`DataFrame.to_stata` which prevented exporting DataFrames to buffers and most file-like objects (:issue:`21041`)
- Bug in :meth:`read_stata` and :class:`StataReader` which did not correctly decode utf-8 strings on Python 3 from Stata 14 files (dta version 118) (:issue:`21244`)
- Bug in IO JSON :func:`read_json` reading empty JSON schema with ``orient='table'`` back to :class:`DataFrame` caused an error (:issue:`21287`)

**Reshaping**

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2 changes: 1 addition & 1 deletion pandas/io/json/table_schema.py
Original file line number Diff line number Diff line change
Expand Up @@ -296,7 +296,7 @@ def parse_table_schema(json, precise_float):
"""
table = loads(json, precise_float=precise_float)
col_order = [field['name'] for field in table['schema']['fields']]
df = DataFrame(table['data'])[col_order]
df = DataFrame(table['data'], columns=col_order)[col_order]

dtypes = {field['name']: convert_json_field_to_pandas_type(field)
for field in table['schema']['fields']}
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13 changes: 13 additions & 0 deletions pandas/tests/io/json/test_json_table_schema.py
Original file line number Diff line number Diff line change
Expand Up @@ -560,3 +560,16 @@ def test_multiindex(self, index_names):
out = df.to_json(orient="table")
result = pd.read_json(out, orient="table")
tm.assert_frame_equal(df, result)

@pytest.mark.parametrize("strict_check", [
pytest.param(True, marks=pytest.mark.xfail), False])
def test_empty_frame_roundtrip(self, strict_check):
# GH 21287
df = pd.DataFrame([], columns=['a', 'b', 'c'])
expected = df.copy()
out = df.to_json(orient='table')
result = pd.read_json(out, orient='table')
# TODO: When DF coercion issue (#21345) is resolved tighten type checks
tm.assert_frame_equal(expected, result,
check_dtype=strict_check,
check_index_type=strict_check)