python - 如何拆分/提取新列并从列中删除提取的字符串

Question

我有一个示例数据框

data = {"col1" : ["1 first 1", "2 second 2", "third 3", "4 fourth 4"]}

df = pd.DataFrame(data)

print(df)


     col1
0   1 first 1
1   2 second 2
2     third 3
3   4 fourth 4

我想提取列中的第一个数字并将其删除

我尝试使用提取

df["index"] = df["col1"].str.extract('(\d)')

    col1       index
0   1 first 1   1
1   2 second 2  2
2   third 3     3
3   4 fourth 4  4

如果我使用replace，我想从col1中删除提取的数字，起始数字和结束数字都将被替换。

所需输出

    col1    index
0   first 1     1
1   second 2    2
2   third 3     NaN
3   fourth 4    4

Answer 1

使用Series.str.replace与 Series.str.extract与 DataFrame.assign分别处理每一列:

#added ^ for start of string
pat = '(^\d)'
df = df.assign(col1 = df["col1"].str.replace(pat, '', regex=True),
               index= df["col1"].str.extract(pat))
print (df)
        col1 index
0    first 1     1
1   second 2     2
2    third 3   NaN
3   fourth 4     4