从列中获取字符串的第一个字母 [英] Get first letter of a string from column

问题描述

我正在和熊猫打架，现在我正在失去.我有与此类似的源表:

I'm fighting with pandas and for now I'm loosing. I have source table similar to this:

import pandas as pd

a=pd.Series([123,22,32,453,45,453,56])
b=pd.Series([234,4353,355,453,345,453,56])
df=pd.concat([a, b], axis=1)
df.columns=['First', 'Second']

我想从列"First"中的值的第一位向该数据帧添加新列: a)将数字从第一"列更改为字符串 b)从新创建的字符串中提取第一个字符 c)来自b的结果另存为数据框中的新列

I would like to add new column to this data frame with first digit from values in column 'First': a) change number to string from column 'First' b) extracting first character from newly created string c) Results from b save as new column in data frame

我不知道如何将其应用于熊猫数据框对象.我将非常感谢您对此的帮助.

I don't know how to apply this to the pandas data frame object. I would be grateful for helping me with that.

推荐答案

将col的dtype投射到str，您可以执行矢量化切片调用str:

Cast the dtype of the col to str and you can perform vectorised slicing calling str:

In [29]:
df['new_col'] = df['First'].astype(str).str[0]
df

Out[29]:
   First  Second new_col
0    123     234       1
1     22    4353       2
2     32     355       3
3    453     453       4
4     45     345       4
5    453     453       4
6     56      56       5

如果需要，可以再次在列上调用astype(int)来回退dtype

if you need to you can cast the dtype back again calling astype(int) on the column

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