unable to add a new column to a pandas dataframe from within a function

Question

it_json are columns that contain lists, for each row in a dataframe I want to add the lists in a fresh column called full

def list_columns(df):
    df2=df.copy()
    for index,row in df.iterrows():
        # print(row)
        l=[]
        if row['it_json_1']:
            l+=row['it_json_1']
        if row['it_json_2']:
            l+=row['it_json_2']
        if row['it_json_3']:
            l+=row['it_json_3']
        if row['it_json_4']:
            l+=row['it_json_4']
        df2['full'][index]= l
    return df2

but list_columns(df) is giving me key error

df2['full'][index]= l command works when there already is a column named 'full'. First we need to create it. df2['full'] = "" in the beginning — The6thSense
– The6thSense, Commented Dec 28, 2022 at 11:07
It is also possible to just add the columns, provided null values are replaced with empty lists. — Sruthi
– Sruthi, Commented Dec 29, 2022 at 5:35

Saksham Sharma · Accepted Answer · 2022-12-28 11:35:23Z

2

You are allocating values to a column that doesn't exist yet, so create an empty column before adding values.

def list_columns(df):
df2=df.copy()
for index,row in df.iterrows():
    # print(row)
    l=[]
    l['full'] = np.nan
    if row['it_json_1']:
        l+=row['it_json_1']
    if row['it_json_2']:
        l+=row['it_json_2']
    if row['it_json_3']:
        l+=row['it_json_3']
    if row['it_json_4']:
        l+=row['it_json_4']
    df2['full'][index]= l
return df2

answered Dec 28, 2022 at 11:35

Saksham Sharma

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Comments

Maen · Accepted Answer · 2022-12-28 11:14:23Z

1

Try to save the values into a list then assign them to the new columns "full"

 full.append(l)

then after the loop ends:

 df2['full'] = full

answered Dec 28, 2022 at 11:14

Maen

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