Indexing the values of the List

Question

I have two different lists with almost the same values but with different index values. I have some values in list_1 and need to extract index of those values in list_2 . Then I want to combine list_1 as ['Number'] column and index outcome as ['Index'] column in a Dataframe.

list_1 = ['1','2','3','4','5','6','7','8','9','10']
list_2 = ['12','11','10','9','8','6','5','4','3','2','1']
data = {"Number":pd.Series(list_1)}
df = pd.Dataframe(data,columns=["Number"])
list_index=[]
for i in df["Number"]:
    if i in list_2:
       index= pd.Index(list_2)
       m = index.get_loc(i)
       list_index.append(m)
df['Index']=list_index

Error is that quantity of values in df["Number"] and list_index are different.

But when I'm trying to add list_1 and m to DataFrame, I can't assign all the dedicated indices to the numbers in list_1 .

Answer 1

First you find the indices of elements in list_2 :

indices = [list_2.index(l) if l in list_2 else None for l in list_1]

I set None when an element is not present in your list_2 but you can put whatever value you desire.

Then, you form the dataframe:

df = pd.DataFrame({'Number': list_1, 'Index': indices})

Output:

    Number  Index
0   1   10.0
1   2   9.0
2   3   8.0
3   4   7.0
4   5   6.0
5   6   5.0
6   7   NaN
7   8   4.0
8   9   3.0
9   10  2.0