Create new dataframe from list of values of variable2 for each value of variable1?

Question

I've got some lists of postcodes from different states, in the form such as

stateA_postcode = [12345, 23456, 34567, ...]
stateB_postcode = [11111, 22222, 33333, ...]

And I would like to create a pandas dataframe like this (order doesn't matter):

     postcode    state
0    11111       B
1    12345       A
...         ...

How to do this?

Answer 1

You can first construct the DataFrame in the wide form and then use melt:

df = pd.DataFrame({'A': stateA_postcode, 'B': stateB_postcode})

pd.melt(df, var_name='state', value_name='postcode')
Out: 
  state  postcode
0     A     12345
1     A     23456
2     A     34567
3     B     11111
4     B     22222
5     B     33333

For different lengths:

stateA_postcode = [12345, 23456, 34567]
stateB_postcode = [11111, 22222]


df = pd.DataFrame({'postcode': stateA_postcode + stateB_postcode,
                   'state': ['A']*len(stateA_postcode) + 
                            ['B']*len(stateB_postcode)})

df
Out: 
   postcode state
0     12345     A
1     23456     A
2     34567     A
3     11111     B
4     22222     B