在 Pandas 数据框中用 NaN 替换字符串值 - Python
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Replace a string value with NaN in pandas data frame - Python
提问by stefanodv
Do I have to replace the value? with NaN so you can invoke the .isnull () method. I have found several solutions but some errors are always returned. Suppose:
我必须更换价值吗？使用 NaN 以便您可以调用 .isnull () 方法。我找到了几种解决方案，但总是返回一些错误。认为：
data = pd.DataFrame([[1,?,5],[?,?,4],[?,32.1,1]])
and if I try:
如果我尝试：
pd.data.replace('?', np.nan)
I have:
我有：
0 1 2
0 1.0 NaN 5
1 NaN NaN 4
2 NaN 32.1 1
but data.isnull() returns:
但 data.isnull() 返回：
0 1 2
0 False False False
1 False False False
2 False False False
Why?
为什么？
回答by jezrael
I think you forget assign back:
我想你忘了分配回来：
data = pd.DataFrame([[1,'?',5],['?','?',4],['?',32.1,1]])
data = data.replace('?', np.nan)
#alternative
#data.replace('?', np.nan, inplace=True)
print (data)
0 1 2
0 1.0 NaN 5
1 NaN NaN 4
2 NaN 32.1 1
print (data.isnull())
0 1 2
0 False True False
1 True True False
2 True False False
回答by caverac
?is a notnull. So you will expect to get a Falseunder the isnulltest
?是不是空。所以你会期望得到一个Falseunder isnulltest
>>> data = pandas.DataFrame([[1,'?',5],['?','?',4],['?',32.1,1]])
>>> data
0 1 2
0 False False False
1 False False False
2 False False False
After you replace ?with NaNthe test will look much different
?用NaN测试替换后看起来会大不相同
>>> data = data.replace('?', np.nan)
>>> data
0 1 2
0 False True False
1 True True False
2 True False False
回答by Som Dubey
I believe when you are doing pd.data.replace('?', np.nan)this action is not done in place, so you must try -
相信你在做pd.data.replace('?', np.nan)这个动作的时候是没有做到位的，所以一定要试试——
data = data.replace('?', np.nan)
