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BUG: non-iterable value in meta raise error in json_normalize #31524

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Merged
merged 33 commits into from
Mar 11, 2020
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BUG: non-iterable value in meta raise error in json_normalize #31524

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remove \n from docstring
charlesdong1991 Dec 3, 2018
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2 changes: 2 additions & 0 deletions doc/source/whatsnew/v1.0.1.rst
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Expand Up @@ -88,6 +88,8 @@ I/O

-
-
- Bug in :meth:`pandas.json_normalize` when value in meta path is not iterable (:issue:`31507`)


Plotting
^^^^^^^^
Expand Down
9 changes: 6 additions & 3 deletions pandas/io/json/_normalize.py
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Expand Up @@ -230,15 +230,18 @@ def _json_normalize(
Returns normalized data with columns prefixed with the given string.
"""

def _pull_field(js: Dict[str, Any], spec: Union[List, str]) -> Iterable:
def _pull_field(
js: Dict[str, Any], spec: Union[List, str], is_meta: bool = True
) -> Any:
result = js # type: ignore
if isinstance(spec, list):
for field in spec:
result = result[field]
else:
result = result[spec]

if not isinstance(result, Iterable):
# GH 31507 iterable limit should only be used on record, not meta
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this is a code smell to add this. so it seems that result can be null, iterabe, or a scalar? if its a scalar what is the return value here?

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you mean [99]? then will still return 99

i think this Iterable should only restrict if specifying record_path, but not for meta? Am I right about the behaviour here @WillAyd ?

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I do agree that this is getting a little strange, especially since there is inspection of meta on line 273 of the same module and we are essentially repeating that here with a boolean indicator being manually supplied

@charlesdong1991 do you see a way to more logically order this function so we don't have to use this bool indicator?

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thanks for your reply! @WillAyd

I will think about it a bit, i feel the patch for that Iterable in this _pull_field has code smell a bit because it is used for two cases which have different requirements

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@charlesdong1991 charlesdong1991 Feb 4, 2020 •
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especially since there is inspection of meta on line 273 of the same module and we are essentially repeating that here with a boolean indicator being manually supplied

i just take a look again at the current codebase, seems that line 273 and onwards you referred is to validate/transform the key which is assigned to meta not the value the key associated with, in this case, key is id (and we could either specify it as [id] or id or more complex cases with nested list, and this part of code will deal with it), however, the code in _pull_field is to pull the value out, and in this case, the value is 99, and for record_path the value should be an Iterable, while for meta it does not necessarily be the case, and therefore I think the patch added to check the type should only work for values of which the element of record_path point to, not for meta, maybe I miss some functionalities of either of them? @WillAyd @jreback

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@charlesdong1991 does splitting this into separate functions for record_path vs meta and just using this as a base for those functions make things cleaner?

if not isinstance(result, Iterable) and not is_meta:
if pd.isnull(result):
result = [] # type: ignore
else:
Expand Down Expand Up @@ -296,7 +299,7 @@ def _recursive_extract(data, path, seen_meta, level=0):
_recursive_extract(obj[path[0]], path[1:], seen_meta, level=level + 1)
else:
for obj in data:
recs = _pull_field(obj, path[0])
recs = _pull_field(obj, path[0], is_meta=False)
recs = [
nested_to_record(r, sep=sep, max_level=max_level)
if isinstance(r, dict)
Expand Down
10 changes: 10 additions & 0 deletions pandas/tests/io/json/test_normalize.py
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Expand Up @@ -749,3 +749,13 @@ def test_series_non_zero_index(self):
}
)
tm.assert_frame_equal(result, expected)

def test_meta_non_iterable(self):
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can you move this near the other test

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moved! and wait for @WillAyd comment on the other one

# GH 31507
data = """[{"id": 99, "data": [{"one": 1, "two": 2}]}]"""

result = json_normalize(json.loads(data), record_path=["data"], meta=["id"])
expected = DataFrame(
{"one": [1], "two": [2], "id": np.array([99], dtype=object)}
)
tm.assert_frame_equal(result, expected)