How to match a pandas DataFrame column consisting of a list?

Question

I have a pandas DataFrame whose column is consisted of a list.

For example:

df = pd.DataFrame({'col1': [['a'], ['b'], ['a'], ['b']]})
df
    col1
0   [a]
1   [b]
2   [a]
3   [b]

I want to select those rows that are ['a'], but if I run this code:

df['col1'] == ['a']

I get an error:

ValueError: ('Lengths must match to compare', (4,), (1,))

(Same to code df[df['col1'] == ['a']] )

What proper code should I use to achieve this?

Answer 1

Try following

df[df['col1'].str[0]=='a']

Answer 2

Use:

df = df[df['col1'].apply(lambda x: x == ['a'])]
print (df)
  col1
0  [a]
2  [a]

Answer 3

You can also convert to a string:

out = df[df['col1'].astype(str) == "['a']"]

Output:

  col1
0  [a]
2  [a]