Question

我有两个列表都包含我要写入csv文件的值。所以我做的第一件事就是将我的csv文件导入到pandas dataframe中。然后我想写两个新列并将这两个列添加到新列中。我的代码如下。请注意，原始csv文件已存在几个列。

import pandas as pd

df = pd.read_csv('1.csv')  ## 1.csv is the csv file I want to import. 


a = [0.001, 5, 38, 70, 101, 140, 190]

b= [35, 65,  100, 160, 170, 200]

df['Start Time'] = a
df['End Time'] = b 

df.to_csv('1.csv')

但是，当我运行此代码时，它给了我一个错误，如下所示，

ValueError: Length of values does not match length of index

如果有人知道如何解决这个问题，请告诉我。感谢！

Answer 1

我认为您首先需要创建Series，但如果长度与NaN的长度不同，则df中的所有最后一个值都会获得DataFrame：

df['Start Time'] = pd.Series(a, index = df.index[:len(a)])
df['End Time'] = pd.Series(b, index = df.index[:len(b)])

样品：

df = pd.DataFrame({'a':range(10)})

a = [0.001, 9, 46, 84, 122, 153, 198]
b= [39, 76,  114, 150, 158, 210]

df['Start Time'] = pd.Series(a, index = df.index[:len(a)])
df['End Time'] = pd.Series(b, index = df.index[:len(b)]) 
print (df)
   a  Start Time  End Time
0  0       0.001      39.0
1  1       9.000      76.0
2  2      46.000     114.0
3  3      84.000     150.0
4  4     122.000     158.0
5  5     153.000     210.0
6  6     198.000       NaN
7  7         NaN       NaN
8  8         NaN       NaN
9  9         NaN       NaN

Answer 2

还可以尝试将a和b的数据类型更改为字符串。这样，NAN值将留为空白。

import pandas as pd

df = pd.read_csv('1.csv')  ## 1.csv is the csv file I want to import. 


a = [0.001, 5, 38, 70, 101, 140, 190]

b = [35, 65,  100, 160, 170, 200]

df['Start Time'] = str(a)
df['End Time'] = str(b) 

df.to_csv('1.csv')

Python：将列表写入Pandas中的列

2 个答案: