pandas 如何遍历数据框中的列？
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How to loop through columns in a dataframe?
提问by analyticsPierce
I have a dataframe with many metric columns all containing float output. I need to round them all to four digits. I want to loop through all the columns to do this.
我有一个包含许多度量列的数据框，所有列都包含浮点输出。我需要将它们全部四舍五入。我想遍历所有列来执行此操作。
import numpy as np
import pandas as pd
test_df = pd.DataFrame(np.random.randn(10,4), columns=['a','b','c','d'])
metrics = test_df.columns
metrics = metrics.tolist()
for x in metrics:
test_df.x = np.round(test_df.x, 4)
However, this gives me the error:
但是，这给了我错误：
AttributeError: 'DataFrame' object has no attribute 'x'
Whats the best way to do this?
什么是最好的方法来做到这一点？
回答by acushner
import functools
test_df.apply(functools.partial(np.round, decimals=4))
if you want to iterate through columns, it's straightforward:
如果你想遍历列，很简单：
for c in test_df.columns:
test_df[c] = np.round(test_df[c], 4)
what you tried to do that's busted has to do with attribute access in python. when you try to do test_df.x, that xhas absolutely nothing to do with the xin your forloop. this would have the same result:
你试图做的事情被破坏了与python中的属性访问有关。当您尝试这样做test_df.x，那x绝对没有任何跟x在你的for循环。这将产生相同的结果：
for unused_value in metrics:
test_df.x = ...
