How to cast a Pandas Dataframe column into 'list' type?

Question

Following the Pandas explode() method documentation, one can explode a list in a row into multiple rows:

df = pd.DataFrame({'A': [[1, 2, 3], 'foo', None, [3, 4]], 'B': 1})
df.explode('A')

However, the DataFrame() I get from a database contains lists that are seen as strings :

df = pd.DataFrame({'A': ["[1, 2, 3]", 'foo', None, "[3, 4]"], 'B': 1})
df.explode('A')
# Does not fail, but does not explode "[1, 2, 3]"

Outside Pandas, I use ast.literal_eval() but don't know how to make it work for my column.

How to cast my 'A' column as list so that explode('A') works ?

ansev · Accepted Answer · 2019-11-28 17:11:45Z

2

You could try with DataFrame.apply:

def f(x):
    try:
        return ast.literal_eval(x)
    except Exception:
        return x


df['A']=df['A'].apply(f)
df.explode('A')

      A  B
0     1  1
0     2  1
0     3  1
1   foo  1
2  None  1
3     3  1
3     4  1

edited Nov 28, 2019 at 17:11

answered Nov 28, 2019 at 17:04

ansev

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3 Comments

anky Over a year ago

use same with literal eval, its safer than eval

ansev Over a year ago

if this does exactly the same thing really

anky Over a year ago

Using python's eval() vs. ast.literal_eval()

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