8000 Column information lost in to_json() if data frame is empty · Issue #7445 · pandas-dev/pandas · GitHub
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Column information lost in to_json() if data frame is empty #7445

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aizvorski opened this issue Jun 12, 2014 · 3 comments
Closed

Column information lost in to_json() if data frame is empty #7445

aizvorski opened this issue Jun 12, 2014 · 3 comments
Labels
Bug IO JSON read_json, to_json, json_normalize
Milestone
0.16.1

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@aizvorski
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Create empty dataframe with a column and write it out with to_json(), then read it back in:

In [55]: s = pandas.DataFrame({'test': [] }, index=[] ).to_json(orient='columns')
In [56]: s
Out[56]: '{}'
In [57]: str( pandas.read_json(s, orient='columns') )
Out[57]: 'Empty DataFrame\nColumns: []\nIndex: []'

I think the expected string is '{"test":{}}'

This situation arises when code filters data frames and writes them out, while not being very careful to make sure the filtered frames contain at least one row.
@jreback jreback added the JSON label Jun 12, 2014
@jreback
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jreback commented Jun 12, 2014

cc @Komnomnomnom

@jreback jreback added the Bug label Jun 12, 2014
@jreback jreback added this to the 0.15.0 milestone Jun 12, 2014
@Komnomnomnom
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Thanks @aizvorski I can confirm this bug, and I agree about the expected output.

The JSON handling is producing its output by looping over the dataframe values array, which is why in this case the labels end up being ignored during serialisation.

@jreback I'm on vacation until mid July but I'll see if I can get this fixed for 0.15. There's also the other JSON issues / features I've been meaning to do since pre 0.14...I'll see if I can knock them out at the same time.

@jreback jreback modified the milestones: 0.16.0, Next Major Release Mar 6, 2015
@behzadnouri
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closed by #9805

>>> pd.DataFrame({'test':[]}, index=[]).to_json(orient='columns')
'{"test":{}}'

mroeschke added a commit to mroeschke/pandas that referenced this issue Dec 16, 2016
@mroeschke
TST: to_json keeps column info with empty dataframe (pandas-dev#7445)
fe2b110
@mroeschke mroeschke mentioned this issue Dec 16, 2016
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@jorisvandenbossche jorisvandenbossche modified the milestones: 0.16.1, Next Major Release Dec 16, 2016
@jreback jreback closed this as completed Dec 16, 2016
mroeschke added a commit to mroeschke/pandas that referenced this issue Dec 16, 2016
@mroeschke
TST: to_json keeps column info with empty dataframe (pandas-dev#7445)
740cafe 
Move test
jreback pushed a commit that referenced this issue Dec 16, 2016
@mroeschke @jreback
TST: to_json keeps column info with empty dataframe (#7445)
2566223 
closes #7445

Author: Matt Roeschke <emailformattr@gmail.com>

Closes #14893 from mroeschke/test_7445 and squashes the following commits:

740cafe [Matt Roeschke] TST: to_json keeps column info with empty dataframe (#7445)
ischurov pushed a commit to ischurov/pandas that referenced this issue Dec 19, 2016
@mroeschke @ischurov
TST: to_json keeps column info with empty dataframe (pandas-dev#7445)
22c4b9a 
closes pandas-dev#7445

Author: Matt Roeschke <emailformattr@gmail.com>

Closes pandas-dev#14893 from mroeschke/test_7445 and squashes the following commits:

740cafe [Matt Roeschke] TST: to_json keeps column info with empty dataframe (pandas-dev#7445)
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Bug IO JSON read_json, to_json, json_normalize
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TST: to_json keeps column info with empty dataframe (#7445) mroeschke/pandas
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@Komnomnomnom @jreback @jorisvandenbossche @behzadnouri @aizvorski
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