[英]Create a new column in pandas using a value of a row
First of all, this is not a duplicate! 首先,这不是重复的! I have searched in several SO questions as well as the Pandas doc, and I have not found anything conclusive!To create a new column with a row value, like this and this ! 我已经搜索了几个SO问题以及Pandas文档,但没有发现任何结论。要创建一个具有行值的新列,例如this和this !
Imagine I have the following table, opening an .xls
and I create a dataframe with it. 想象一下,我有下表, 打开一个.xls
然后用它创建一个数据框。 As this is a small example created from the real proble, I created this simple Excel table which can be easily reproduceable: 因为这是从实际问题中创建的一个小示例,所以我创建了这个简单的Excel表,该表可以轻松复制:
What I want now is to find the row that has "Population Month Year"
(I will be looking at different .xls
, so the structure is the same: population, month and year. 我现在想要的是找到具有"Population Month Year"
(我将查看不同的.xls
,因此结构是相同的:人口,月份和年份。
xls='population_example.xls'
sheet_name='Sheet1'
df = pd.read_excel(xls, sheet_name=sheet_name, header=0, skiprows=2)
df
What I thought is: 我以为是:
Get the value of that row with startswith
使用startswith
获取该行的值
Create a column, pythoning that value and getting the month and year value. 创建一列,使用该值进行Python处理并获取月份和年份的值。
I have tried several things similar to this: 我已经尝试过类似的几件事:
dff=df[s.str.startswith('Population')]
dff
But errors won't stop coming. 但是错误不会停止。 In this above's code error, specifically: 在上面的代码错误中,具体是:
IndexingError: Unalignable boolean Series provided as indexer (index of the boolean Series and of the indexed object do not match IndexingError:作为索引器提供的不可对齐的布尔系列(布尔系列的索引与索引对象的索引不匹配
I have several guesses: 我有几个猜测:
Series
in pandas work, even though reading the doc. 即使阅读文档,我也无法正确理解熊猫Series
的工作原理。 I did not even think on using them, but the startswith
looks like the thing I am looking for. 我什至没有想到要使用它们,但是startswith
看起来就像我想要的东西。 NaN error
, but I cannot use df.dropna()
yet, as I would lose that row value ( Population April 2017
)! 如果我处理正确,可能会出现NaN error
,但是我仍然不能使用df.dropna()
,因为我会丢失该行值(《 Population April 2017
)! Edit: 编辑:
The problem on using this: 使用此问题:
df[df['Area'].str.startswith('Population')]
Is that it will check the na values
. df[df['Area'].str.startswith('Population')]
是它将检查na values
。
And this: 和这个:
df['Area'].str.startswith('Population')
Will give me a true/false/na set of values, which I am not sure how I can use. 会给我一个true / false / na的值集,我不确定该如何使用。
Thanks to @Erfan , I got to the solution: 感谢@Erfan,我找到了解决方案:
Using properly the line of code in the comments and not like I was trying, I managed to: 正确使用注释中的代码行,而不是像我尝试的那样,我设法:
dff=df[df['Area'].str.startswith('Population', na=False)] dff
Which would output: Population and household forecasts, 2016 to 20... NaN NaN NaN NaN NaN NaN
将会输出: Population and household forecasts, 2016 to 20... NaN NaN NaN NaN NaN NaN
Now I can access this value like 现在我可以像这样访问该值
value=dff.iloc[0][0] value
To get the string I was looking for: 'Population and household forecasts, 2016 to 2041, prepared by .id , the population experts, April 2019.'
为了得到我一直在寻找的字符串, 'Population and household forecasts, 2016 to 2041, prepared by .id , the population experts, April 2019.'
And I can python around with this to create the desired column. 我可以用python来创建所需的列。 Thank you! 谢谢!
You could try: 您可以尝试:
import pandas as pd
import numpy as np
pd.DataFrame({'Area': [f'Whatever{i+1}' for i in range(3)] + [np.nan, 'Population April 2017.'],
'Population': [3867, 1675, 1904, np.nan, np.nan]}).to_excel('population_example.xls', index=False)
df = pd.read_excel('population_example.xls').fillna('')
population_date = df[df.Area.str.startswith('Population')].Area.values[0].lstrip('Population ').rstrip('.').split()
Result: 结果:
['April', '2017']
Or (if Population Month Year is always on the last row): 或(如果“人口月份”始终在最后一行):
df.iloc[-1, 0].lstrip('Population ').rstrip('.').split()
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