大熊猫：根据列值重构数据框

Question

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

Answer 1

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