当dataframe元素的值是列表时如何使用.loc [python pandas] [英] How to use .loc when the value of dataframe elements are list [python pandas]
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问题描述
我有一个数据框df
,其中df.trajec
中的元素是一个列表.
I have a dataframe df
where the elements in df.trajec
is a list.
例如df.ix['smith']['trajec'] = ['a', 'b', 'c', 'a', 'b']
type(df.ix['smith']) = list
在这种情况下,我发现我无法使用该命令.
In this case, I found out that I cannot use such command.
aaa = ['a', 'b', 'c', 'a', 'b']
df.loc[df.trajec == aaa]
它给了我以下错误消息.
And it gives me an error message like below.
ValueError: Arrays were different lengths: 8886 vs 5
有什么方法可以找到数据帧df
的子集,其中df.trajec
等于列表aaa
吗?
Is there any way to find the subset of the dataframe df
where df.trajec
is equal to a list aaa
?
推荐答案
您需要 apply
用于创建mask
:
df = pd.DataFrame({'trajec':[['a', 'b', 'c', 'a', 'b'],
['a', 'b'],
['a','c', 'b']]},
index=['smith','smith1','smith2'])
print (df)
trajec
smith [a, b, c, a, b]
smith1 [a, b]
smith2 [a, c, b]
aaa = ['a', 'b', 'c', 'a', 'b']
mask = df.trajec.apply(lambda x: x == aaa)
print (mask)
smith True
smith1 False
smith2 False
Name: trajec, dtype: bool
#loc can be omit if need filter all columns
print (df[mask])
trajec
smith [a, b, c, a, b]
#if need apply mask and return only column `trajec`
print (df.loc[mask, 'trajec'])
smith [a, b, c, a, b]
Name: trajec, dtype: object
另一个可能的mask
是list comprehension
:
mask = [x == aaa for x in df.trajec.values]
print (mask)
[True, False, False]
print (df[mask])
trajec
smith [a, b, c, a, b]
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