Strange output from `DataFrame.apply` when applied func creates a dict

[onesandzeroes]

Just had something odd come up while trying to come up with something for this SO question.

If we use DataFrame.apply() to try and create dictionaries from the rows of a dataframe, it seems to return the dict.values() method rather than returning the dict itself.

df = pd.DataFrame({'k': ['a', 'b', 'c'], 'v': [1, 2, 3]})
df.apply(lambda row: {row['k']: row['v']}, axis=1)
Out[52]: 
0    <built-in method values of dict object at 0x07...
1    <built-in method values of dict object at 0x03...
2    <built-in method values of dict object at 0x07...
dtype: object

Looks like it's probably something to do with trying to grab the values attribute when the output of the applied function is a Series or something similar.

Library versions:

pd.show_versions()
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.6.final.0
python-bits: 32
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 30 Stepping 5, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None

pandas: 0.15.0
nose: 1.3.4
Cython: 0.21
numpy: 1.9.0
scipy: 0.14.0
statsmodels: 0.5.0
IPython: 2.3.0
sphinx: 1.2.3
patsy: 0.3.0
dateutil: 1.5
pytz: 2014.7
bottleneck: None
tables: 3.1.1
numexpr: 2.3.1
matplotlib: 1.4.2
openpyxl: 1.8.5
xlrd: 0.9.3
xlwt: 0.7.5
xlsxwriter: 0.5.7
lxml: 3.4.0
bs4: 4.3.2
html5lib: 0.999
httplib2: None
apiclient: None
rpy2: None
sqlalchemy: 0.9.7
pymysql: None
psycopg2: None

[jreback]

This inference is done in cython. It is indeed trying to get the values attribute (e.g. _values_from_object). I suppose you could fix it.

Do you want something like this?

In [1]: df = pd.DataFrame({'k': ['a', 'b', 'c'], 'v': [1, 2, 3]})

In [2]: def f(row):
   ...:         return pd.Series({row['k']: row['v']})
   ...: 

In [3]: df.apply(f,axis=1)
Out[3]: 
    a   b   c
0   1 NaN NaN
1 NaN   2 NaN
2 NaN NaN   3

[ringw]

Hi all, I've run into the same issue myself. I actually need to pass a list of dicts for each row as my output, and it would be nice to be able to do list(df.apply(lambda x: x.to_dict(), 0)). This would require df.apply to return a Series of dtype object, where the elements are dicts.

apply returning a Series of dicts would be consistent with the behavior when the passed function returns an object Pandas doesn't understand (apparently, any non-numeric without a values attribute). I guess I can add a check to _values_from_object to make sure the input is, say, a subclass of PandasObject.

[Casyfill]

Hey, I still have this issue with my function returing a dict as part of aggregation

[jreback]

well this was fixed in 0.17.0