Merge lists is multiple columns of a pandas dataframe into a sigle list in a column

Question

I have a dataframe with two columns containing lists. I want to combine these columns into a single column and merge the lists into a single list. Also this list should only contain unique values from the original lists.

I've tried merging them using df['E']=df[['B','C']].values.tolist().

However this creates a single column with values comprising two lists.

The dataframe looks something like this:

A       B       C       D
a1      [b1,b2] [c1,b1] d1
a2      [b1,b1] [b3]    d2
a3      [b2]    [b2,b2] d3

The final dataframe should look like this:

A       B       C       D       E
a1      [b1,b2] [c1,b1] d1      [b1,b2,c1]
a2      [b1,b1] [b3]    d2      [b1,b3]
a3      [b2]    [b2,b2] d3      [b2]

Edit: The values within the lists of the dataframe are strings.

Answer 1

IIUC

df['E']=(df.B+df.C).map(set).map(list)
df
Out[81]: 
    A         B         C   D             E
0  a1  [b1, b2]  [c1, b1]  d1  [b2, b1, c1]
1  a2  [b1, b1]      [b3]  d2      [b3, b1]
2  a3      [b2]  [b2, b2]  d3          [b2]