pandas dataframe index: to_list() vs tolist()

Question

I recently wrote a python script for someone, where I converted a pandas dataframe's index into a list using to_list(). However, this does not work for them, as they get: AttributeError: 'Index' object has no attribute 'to_list' with their python interpretter.

I did some searching and found that there is also tolist() that seems to do the same as to_list(): searching on Pandas documentation finds both, with word-for-word identical description. On the other hand, the documentation of Index mentions only to_list().

So I wonder whether there is a difference between the two

in functionality
in popularity and/or "officiality"/endorsement
in support in different version of pandas

buran · Accepted Answer · 2020-09-02 13:30:51Z

42

If you check the source code, you will see that right after tolist() code there is line to_list = tolist, so to_list is just alias for tolist

EDIT: to_list() was added in ver. 0.24.0, see issue#8826

edited Sep 2, 2020 at 13:30

answered Sep 9, 2019 at 12:47

buran

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Michal Kaut · Accepted Answer · 2019-09-09 14:09:30Z

Expanding on buran's answer (too much text to fit into a comment): Using git blameon the pointed-out source code, one can see that to_list() was indeed added in December 2018 as an alias to tolist(). It was commited as an enhancement to resolve issue 8826, i.e., to make it more inline with to_period() and to_timestamp().

Moreover, changes and comments in pandas/core/series.py show that the original tolist() is "semi-deprecated":

# tolist is not actually deprecated, just suppressed in the __dir__
_deprecations = generic.NDFrame._deprecations | frozenset(
    ['asobject', 'reshape', 'get_value', 'set_value',
     'from_csv', 'valid'])
     'from_csv', 'valid', 'tolist'])

Interesting to see how the system works...

edornd · Accepted Answer · 2019-09-09 12:45:29Z

4

This question would need a pandas developer to be answered without doubts, but a reasonable guess would be that it serves as support for legacy versions. As you can see from the source code here, the 'source' button for to_list forwards to the same source code of tolist, and the two functions are simply aliases.

answered Sep 9, 2019 at 12:45

edornd

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Himanshu Shrimalve · Accepted Answer · 2022-07-05 14:24:12Z

1

With all the above answers, only thing which we can get is that to_list() is just a alias of original tolist(). I do noticed a difference though: while converting a pandas.DataFrame() created with dict consisting numpy.ndarray, to_list throws an error AttributeError: 'numpy.ndarray' object has no attribute 'to_list', whereas tolist did the job.

dict = {'Name':['Martha', 'Tim', 'Rob', 'Georgia'],
        'Maths':[87, 91, 97, 95],
        'Science':[83, 99, 84, 76]
       }
df = pd.DataFrame(dict)

output['OP.pool_results'] = df.values.to_list()

output:

Traceback (most recent call last):

  File "C:\Users\hshrima\AppData\Local\Temp/ipykernel_24028/1619690827.py", line 1, in <module>
    df.values[0].to_list()

AttributeError: 'numpy.ndarray' object has no attribute 'to_list'

But, if I use tolist, following is the result

df.values.tolist()
[['Martha', 87, 83], ['Tim', 91, 99], ['Rob', 97, 84], ['Georgia', 95, 76]]

Here, tolist refers to ndarray.tolist, whereas the above to_list refers to IndexOpsMixin.tolist from pandas

edited Jul 5, 2022 at 14:24

answered Jul 5, 2022 at 13:48

Himanshu Shrimalve

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1 Comment

Michal Kaut Over a year ago

Note that the question was about pandas tolist vs to_list. pandas.DataFrame.values returns a numpy array and numpy indeed has only tolist. Indeed, if you read the discussion about the issue linked in the accepted answer, numpy's tolink is the reason why pandas used tolink and why they did not deprecate it after introducing to_list...

moken · Accepted Answer · 2023-08-05 14:44:07Z

1

In Python;
tolist() is a method of NumPy arrays that returns a list representation of the array.
to_list() is a method of Pandas dataframes that returns a list representation of the dataframe.

Although both methods return the same output, their differences lie in their origins and compatibility. *to_list()* is Pandas-specific.

edited Aug 5, 2023 at 14:44

moken

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answered Aug 2, 2023 at 14:34

Ramin Eslami

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mirekphd · Accepted Answer · 2024-08-01 07:28:34Z

0

I'm afraid Pandas created a confusion here, because .to_list() is not / no longer an alias in NumPy (it will raise an AttributeError), so you should use .tolist() (and other "to" methods) without an underscore. While I'm not denying that the to_list alias might have worked, it was undocumented even as far as the NumPy docs on numpy.ndarray.tolist go back, i.e. in v1.13 (released in 2017).

answered Aug 1, 2024 at 7:28

mirekphd

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2 Comments

Michal Kaut Over a year ago

Again, the question is about pandas, not numpy. In pandas, both versions exist and the accepted answer is still true.

mirekphd Over a year ago

Yeah, I do realize its about pandas, just wanted to spare others the surprising lack of user-friendliness in numpy which is a bit too opinionated here. And to_list is even more pythonic too (as per PEP-8 naming conventions).

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