Pandas - combine column values into a list in a new column

问题

I have a Python Pandas dataframe df:

d=[['hello',1,'GOOD','long.kw'],
   [1.2,'chipotle',np.nan,'bingo'],
   ['various',np.nan,3000,123.456]]                                                    
t=pd.DataFrame(data=d, columns=['A','B','C','D'])

which looks like this:

print(t)
         A         B     C        D
0    hello         1  GOOD  long.kw
1      1.2  chipotle   NaN    bingo
2  various       NaN  3000  123.456

I am trying to create a new column which is a list of the values in A, B, C, and D. So it would look like this:

t['combined']                                             

Out[125]: 
0        [hello, 1, GOOD, long.kw]
1        [1.2, chipotle, nan, bingo]
2        [various, nan, 3000, 123.456]
Name: combined, dtype: object

I am trying this code:

t['combined'] = t.apply(lambda x: list([x['A'],
                                        x['B'],
                                        x['C'],
                                        x['D']]),axis=1)

Which returns this error:

ValueError: Wrong number of items passed 4, placement implies 1

What is puzzling to me is if remove one of the columns that I want to put in the list (or add another column to the dataframe that I DON'T add to the list), my code works.

For instance, run this code:

t['combined'] = t.apply(lambda x: list([x['A'],
                                        x['B'],
                                        x['D']]),axis=1)

Returns this which is perfect if I only wanted the 3 columns:

print(t)
         A         B     C        D                 combined
0    hello         1  GOOD  long.kw      [hello, 1, long.kw]
1      1.2  chipotle   NaN    bingo   [1.2, chipotle, bingo]
2  various       NaN  3000  123.456  [various, nan, 123.456]

I am at a complete loss as to why requesting the 'combined' list be made of all columns in the dataframe would create an error, but selecting all but 1 column to create the 'combined' list and the list is created as expected.

回答1:

try this :

t['combined']= t.values.tolist()

t
Out[50]: 
         A         B     C        D                       combined
0    hello         1  GOOD  long.kw      [hello, 1, GOOD, long.kw]
1     1.20  chipotle   NaN    bingo    [1.2, chipotle, nan, bingo]
2  various       NaN  3000   123.46  [various, nan, 3000, 123.456]

来源：https://stackoverflow.com/questions/43898035/pandas-combine-column-values-into-a-list-in-a-new-column

标签

python

list

pandas

lambda

apply