Python 在 Pandas 中添加计算列
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Adding calculated column in Pandas
提问by JD2775
I have a dataframe with 10 columns. I want to add a new column 'age_bmi' which should be a calculated column multiplying 'age' * 'bmi'. age is an INT, bmi is a FLOAT.
我有一个包含 10 列的数据框。我想添加一个新列 'age_bmi'，它应该是一个乘以 'age' * 'bmi' 的计算列。age 是一个 INT，bmi 是一个 FLOAT。
That then creates the new dataframe with 11 columns.
然后创建具有 11 列的新数据框。
Something I am doing isn't quite right. I think it's a syntax issue. Any ideas?
我正在做的事情并不完全正确。我认为这是一个语法问题。有任何想法吗？
Thanks
谢谢
df2['age_bmi'] = df(['age'] * ['bmi'])
print(df2)
回答by Cory Madden
try df2['age_bmi'] = df.age * df.bmi.
试试df2['age_bmi'] = df.age * df.bmi。
You're trying to call the dataframe as a function, when you need to get the values of the columns, which you can access by key like a dictionary or by property if it's a lowercase name with no spaces that doesn't match a built-in DataFrame method.
您正在尝试将数据框作为函数调用，当您需要获取列的值时，您可以通过键（如字典）或属性（如果它是一个没有空格的小写名称与内置的不匹配）访问这些值-in DataFrame 方法。
Someone linked this in a comment the other day and it's pretty awesome. I recommend giving it a watch, even if you don't do the exercises: https://www.youtube.com/watch?v=5JnMutdy6Fw
前几天有人在评论中链接了这个，这非常棒。即使你不做练习，我也建议给它一块手表：https: //www.youtube.com/watch?v=5JnMutdy6Fw
回答by Zero
As pointed by Cory, you're calling a dataframe as a function, that'll not work as you expect. Here are 4 ways to multiple two columns, in most cases you'd use the first method.
正如 Cory 所指出的，您将数据帧作为函数调用，这不会像您预期的那样工作。这里有 4 种方法可以多列两列，在大多数情况下，您会使用第一种方法。
In [299]: df['age_bmi'] = df.age * df.bmi
or,
或者，
In [300]: df['age_bmi'] = df.eval('age*bmi')
or,
或者，
In [301]: df['age_bmi'] = pd.eval('df.age*df.bmi')
or,
或者，
In [302]: df['age_bmi'] = df.age.mul(df.bmi)
