Creating Python Column based on List of list value

Question

I have a list of list and a dataframe df:

test_list=[[A,B,C],[A,B,D],[A,B,E],[F,G]]

and dataframe is

ID
 B
 C
 D
 E

The element of List of list represent hierarchy .I want to create a new column "type" in the dataframe whose value represent its parent.

My final Dataframe should be like:

value  parent
    B       A
    C       B 
    D       B
    E       B

I have a very large dataset and test_list is also very large

Can you elaborate on the logic from the list to the parent? Why is A the parent of B? What if your test list is screwed up, e.g. test_list=[[A,B,C], [D,B,C]]? Would the previous case mean that the parent of B is both A and D? How do you want to handle pathological cases like this? — Spinor8
– Spinor8, Commented May 17, 2019 at 8:29
@Spinor8 My test_list will never screwed up that is sure .yes parent of B is A not D. (that case will never occur) — sourav khanna
– sourav khanna, Commented May 17, 2019 at 8:32
If that's the case, it is relatively straightforward. Traverse the list and generate a dictionary. Then convert the dictionary into the dataframe. — Spinor8
– Spinor8, Commented May 17, 2019 at 8:43

Spinor8 · Accepted Answer · 2019-05-17 08:58:35Z

2

As per my comments on using a dictionary, here's the code.

import pandas as pd
test_list=[["A","B","C"],["A","B","D"],["A","B","E"],["F","G"]]

dict = {}
for sublist in test_list:
    for n, elem in enumerate(sublist):
        if n != 0:
            dict[elem] = prev
        prev = elem

df = pd.DataFrame([dict.keys(), dict.values()]).T
df.columns= ['element', 'parent']
df.set_index('element', inplace=True)
print(df)

giving the following output.

        parent
element       
B            A
C            B
D            B
E            B
G            F

answered May 17, 2019 at 8:58

Spinor8

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Comments

marc_s · Accepted Answer · 2019-11-05 22:11:48Z

1

You could use a dictionary. Here is a working example :

df = pd.DataFrame({'ID': ['B', 'C', 'D', 'E']})
test_list=[['A','B','C'],['A','B','D'],['A','B','E'],['F','G']]

parent = {}
for element in test_list:
    for i in range(len(element)-1):
        parent[element[i+1]] = element[i]

df['parent'] = [parent[x] for x in df['ID']]

In [1] : print(df)
Out[1] :  ID parent
0  B      A
1  C      B
2  D      B
3  E      B

edited Nov 5, 2019 at 22:11

marc_s

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answered May 17, 2019 at 8:50

vlemaistre

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