Python 如何在 Pandas 的特定列索引处插入一列？
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how do I insert a column at a specific column index in pandas?
提问by HappyPy
Can I insert a column at a specific column index in pandas?
我可以在 Pandas 的特定列索引处插入一列吗？
import pandas as pd
df = pd.DataFrame({'l':['a','b','c','d'], 'v':[1,2,1,2]})
df['n'] = 0
This will put column nas the last column of df, but isn't there a way to tell dfto put nat the beginning?
这会将列n作为 的最后一列df，但是没有办法告诉df将放在n开头吗？
采纳答案by Jeff
see docs: http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.insert.html
见文档：http: //pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.insert.html
using loc = 0 will insert at the beginning
使用 loc = 0 将在开头插入
df.insert(loc, column, value)
df = pd.DataFrame({'B': [1, 2, 3], 'C': [4, 5, 6]})
df
Out:
B C
0 1 4
1 2 5
2 3 6
idx = 0
new_col = [7, 8, 9] # can be a list, a Series, an array or a scalar
df.insert(loc=idx, column='A', value=new_col)
df
Out:
A B C
0 7 1 4
1 8 2 5
2 9 3 6
回答by Nic
You could try to extract columns as list, massage this as you want, and reindex your dataframe:
您可以尝试将列提取为列表，根据需要对其进行按摩，然后重新索引您的数据框：
>>> cols = df.columns.tolist()
>>> cols = [cols[-1]]+cols[:-1] # or whatever change you need
>>> df.reindex(columns=cols)
n l v
0 0 a 1
1 0 b 2
2 0 c 1
3 0 d 2
EDIT: this can be done in one line ; however, this looks a bit ugly. Maybe some cleaner proposal may come...
编辑：这可以在一行中完成；然而，这看起来有点难看。也许一些更清洁的建议可能会出现......
>>> df.reindex(columns=['n']+df.columns[:-1].tolist())
n l v
0 0 a 1
1 0 b 2
2 0 c 1
3 0 d 2
回答by Hugo Vares
If you want a single value for all rows:
如果您想要所有行的单个值：
df.insert(0,'name_of_column','')
df['name_of_column'] = value
Edit:
编辑：
You can also:
你也可以：
df.insert(0,'name_of_column',value)
