The pandas dataframe includes two columns 'A' and 'B'
A B
1 a b
2 a c d
3 x
Each value in column 'B' is a string containing a variable number of letters separated by spaces.
Is there a simple way to construct:
A B
1 a
1 b
2 a
2 c
2 d
3 x
You can use the following:
splitted = df.set_index("A")["B"].str.split(expand=True)
stacked = splitted.stack().reset_index(1, drop=True)
result = stacked.to_frame("B").reset_index()
print(result)
A B
0 1 a
1 1 b
2 2 a
3 2 c
4 2 d
5 3 x
For the sub steps, see below:
print(splitted)
0 1 2
A
1 a b None
2 a c d
3 x None None
print(stacked)
A
1 a
1 b
2 a
2 c
2 d
3 x
dtype: object
Or you may also use pd.melt:
splitted = df["B"].str.split(expand=True)
pd.melt(splitted.assign(A=df.A), id_vars="A", value_name="B")\
.dropna()\
.drop("variable", axis=1)\
.sort_values("A")
A B
0 1 a
3 1 b
1 2 a
4 2 c
7 2 d
2 3 x
