Use DataFrame.stack with Series.explode for convert lists, last some data cleaning with DataFrame.reset_index:
df1 = (df.set_index('col1')
.stack()
.explode()
.reset_index(level=1, drop=True)
.reset_index(name='value'))
Alternative with DataFrame.melt and DataFrame.explode:
df1 = (df.melt('col1')
.explode('value')
.sort_values('col1')[['col1','value']]
.reset_index(drop=True)
)
print (df1)
col1 value
0 1 blue
1 1 in
2 1 out
3 2 green
4 2 green
5 2 in
6 3 green
7 3 in
Or list comprehension solution:
L = [(k, x) for k, v in df.set_index('col1').to_dict('index').items()
for k1, v1 in v.items()
for x in v1]
df1 = pd.DataFrame(L, columns=['col1','value'])
print (df1)
col1 value
0 1 blue
1 1 in
2 1 out
3 2 green
4 2 green
5 2 in
6 3 green
7 3 in