从列表列表中提取元素 - Python Pandas

Question

I have the following pandas dataframe with only one column:

          column_name
0   cc_call_center_sk
1   cc_call_center_id
2   cc_rec_start_date
3     cc_rec_end_date

What I want to do is to extract each element inside that pandas column and put it into a string like this:

my_string = ['cc_call_center_sk', 'cc_call_center_id', 'cc_rec_start_date', 
'cc_rec_end_date']

I tried to do this with the following code:

my_list = column_names.values.tolist()

However, the output is a list and it is not as desired:

[['cc_call_center_sk'], ['cc_call_center_id'], ['cc_rec_start_date'], ['cc_rec_end_date']]

Answer 1

The df.names.tolist() generates the expected result:

>>> df.name.tolist()
['cc_call_center_sk', 'cc_call_center_id', 'cc_rec_start_date', 'cc_rec_end_date']

For example:

>>> df=pd.DataFrame([['cc_call_center_sk'], ['cc_call_center_id'], ['cc_rec_start_date'], ['cc_rec_end_date']], columns=['names'])
>>> df
               names
0  cc_call_center_sk
1  cc_call_center_id
2  cc_rec_start_date
3    cc_rec_end_date
>>> df = pd.DataFrame([['cc_call_center_sk'], ['cc_call_center_id'], ['cc_rec_start_date'], ['cc_rec_end_date']], columns=['names'])
>>> df.names.tolist()
['cc_call_center_sk', 'cc_call_center_id', 'cc_rec_start_date', 'cc_rec_end_date']

are you sure you do not "group" values, or perform other "preprocessing" before obtaining the df.names ?

Answer 2

You can use the tolist method on the 'column_name' series. Note that my_string is a list of strings , not a string. The name you have assigned is not appropriate.

>>> import pandas as pd
>>> df = pd.DataFrame(['cc_call_center_sk', 'cc_call_center_id', 'cc_rec_start_date', 'cc_rec_end_date'],
...                   columns=['column_name'])
>>> df
         column_name
0  cc_call_center_sk
1  cc_call_center_id
2  cc_rec_start_date
3    cc_rec_end_date
>>>
>>> df['column_name'].tolist()
['cc_call_center_sk', 'cc_call_center_id', 'cc_rec_start_date', 'cc_rec_end_date']

If you prefer the dot notation, the following code does the same.

>>> df.column_name.tolist()
['cc_call_center_sk', 'cc_call_center_id', 'cc_rec_start_date', 'cc_rec_end_date']

Answer 3

Lets say you have a data frame named df which looks like this:

df
    column_name
0   cc_call_center_sk
1   cc_call_center_id
2   cc_rec_start_date
3   cc_rec_end_date

then:

my_string = df.column_name.values.tolist()

or:

my_string = df['column_name'].values.tolist()

would give you the result that you want. Here is the result when you print my_string

['cc_call_center_sk',
'cc_call_center_id',
'cc_rec_start_date',
'cc_rec_end_date']

What you are trying to do is this:

my_strings = df.values.tolist()

This would give you a list of lists with the number of lists in the outer list being equal to the number of observations in your data frame. Each list would contain all the feature information pertaining to 1 observation.

I hope I was clear in explaining that to you. Thank you