Python 如何逐个组合分组文本

我有一个如下所示的数据帧

        text  group
0      hello      1
1      world      1
2       it's      2
3       time      2
4         to      2
5    explore      2
6        one      3
7       more      3
8       line      3

        text  group                     result
0      hello      1                      hello
1      world      1                hello world
2       it's      2                       it's
3       time      2                  it's time
4         to      2               it's time to
5    explore      2       it's time to explore
6        one      3                        one
7       more      3                   one more
8       line      3              one more line

我想把文本中的每个单词一个接一个地组合在新的列中，如下所示

        text  group
0      hello      1
1      world      1
2       it's      2
3       time      2
4         to      2
5    explore      2
6        one      3
7       more      3
8       line      3

        text  group                     result
0      hello      1                      hello
1      world      1                hello world
2       it's      2                       it's
3       time      2                  it's time
4         to      2               it's time to
5    explore      2       it's time to explore
6        one      3                        one
7       more      3                   one more
8       line      3              one more line

到目前为止我试过

df['res']=df.groupby('group')['text'].transform(lambda x: ' '.join(x))
df['result']=df[['text','res']].apply(lambda x: ' '.join( x['res'].split()[:x['res'].split().index(x['text'])+1]),axis=1)

上述代码适用于上述问题。但它也有一些问题

若我有重复的文本索引将给我第一个元素的位置，它失败的数据

        text  group                     result
0      hello      1                      hello
1      world      1                hello world
2       it's      2                       it's
3       time      2                  it's time
4         to      2               it's time to
5    explore      2       it's time to explore
6        one      3                        one
7       more      3                   one more
8       line      3              one more line
9      hello      4                      hello
10  repeated      4             hello repeated
11     hello      4                      hello #this must be hello repeated hello
12      came      4  hello repeated hello came

注意：在第4组失败

而且我的剧本显然是无效的

有人能提出一种解决我的索引问题和性能问题的方法吗

---

任何帮助都是值得赞赏的。

使用

字符串
的函数
cumsum
并不容易，但这里有一个可能的解决方案-首先在末尾添加空间，最后通过以下方式从右侧移除空间：

备选方案：

df['res'] = df['text'].add(' ').groupby(df['group']).transform(pd.Series.cumsum).str.rstrip()


另一个解决方案：

f = lambda x: [' '.join(x[:i]) for i in range(1, len(x)+1)]
df['res'] = df.groupby('group')['text'].transform(f)

在列表理解中使用
groupby
：

df['res'] = [' '.join(d.text[:i]) for _, d in df.groupby('group') for i in range(1, len(d)+1)]

print(df)
        text  group                        res
0      hello      1                      hello
1      world      1                hello world
2       it's      2                       it's
3       time      2                  it's time
4         to      2               it's time to
5    explore      2       it's time to explore
6        one      3                        one
7       more      3                   one more
8       line      3              one more line
9      hello      4                      hello
10  repeated      4             hello repeated
11     hello      4       hello repeated hello
12      came      4  hello repeated hello came