TypeError during iterations within while loop

Question

I am having some troubles with an assigned task. I have tried to figure it out where the error is, but still with no success. I have the following (small, just for example) dataset:

T1              T2                     V1       V2
name_1  ['name_3', 'name_4']          [1,2]   ['a','b']
name_2  []                            []      []
name_3  ['name_1']                    [1]     ['c']
name_4  ['name_1','name_x','name_13'] [12,2,4] ['c','NA','d']
name_4  ['name_1','name_x','name_13'] [12,2,4] ['c','NA','d']

Since T2, V1 and V2 are shown as lists, I had to use explode() and create two new variables, new_t2 and new_t1, to check what values from those columns are still missing and need to be checked.

df = df.explode('T2')

getting the following error (caused within a function that I am going to discuss later in this post):

TypeError: string indices must be integers

Many thanks for your help.

Nk03 · Accepted Answer · 2021-04-12 15:09:00Z

Here's the solution from what I understood -

1st you can flatten the dataframe to make easy calculations this can be done via(use ast.literal_eval only when explode doesn't work directly)

from ast import literal_eval
for col in df.columns.values[1:]:
    df[col] = df[col].apply(literal_eval) #convert to list type
df = df.set_index(['T1']).apply(pd.Series.explode).reset_index()

The operation will flatten the dataframe like this -

T1	T2	V1	V2
name_1	name_3	1	a
name_1	name_4	2	b
name_2	NaN	NaN	NaN
name_3	name_1	1	c
name_4	name_1	12	c
name_4	name_x	2	NA
name_4	name_13	4	d
name_4	name_1	12	c
name_4	name_x	2	NA
name_4	name_13	4	d

Now, if you want tuples for only those rows in 'T2' which are not there in 'T1'. You can use apply or something else. I used apply-

unique_t1 = set(df['T1'].to_list())
def tuple_creation(x):
    if x['T2'] not in unique_t1:
        return (x['T2'],x['V1'],x['V2']) #if you want to add T1 in the tuple just add it here.
df['tuple'] = df.apply(lambda x: tuple_creation(x), axis=1)

Output (for display I've transformed tuple to '-' separated string)-

T1	T2	V1	V2	tuple
name_1	name_3	1	a
name_1	name_4	2	b
name_2				nan-nan-nan
name_3	name_1	1	c
name_4	name_1	12	c
name_4	name_x	2	NA	name_x-2-NA
name_4	name_13	4	d	name_13-4-d
name_4	name_1	12	c
name_4	name_x	2	NA	name_x-2-NA
name_4	name_13	4	d	name_13-4-d

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