pandas :如何使用应用功能到多个列 [英] Pandas: How to use apply function to multiple columns
问题描述
df = DataFrame({ 'a':np.random.randn(6),
'b':['foo','bar'] * 3,
'c':np.random.randn(6)} )
和以下功能
def my_test(a,b):
return a%b
当我尝试应用此功能时:
df ['Value'] = df.apply(lambda row: my_test(row [a],row [c]),axis = 1)
消息:
NameError:(全局名称a'未定义,您在索引0'中出现)
我不明白这个消息,我正确地定义了这个名字。
非常感谢在这个问题上的任何帮助
更新
感谢您的帮助。我确实有一些语法错误与代码,索引应该放在''。然而,我仍然使用一个更复杂的功能,如:
def my_test(a):
cum_diff = d $ d
$ d $ cum cum c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c $ c>
谢谢
忘了你的字符串的''
。
在[43]中: df ['Value'] = df.apply(lambda row:my_test(row ['a'],row ['c']),axis = 1)
在[44]中:df
出[44]:
abc价值
0 -1.674308 foo 0.343801 0.044698
1 -2.163236 bar -2.046438 -0.116798
2 -0.199115 foo -0.458050 -0.199115
3 0.918646 bar -0.007185 -0.001006
4 1.336830 foo 0.534292 0.268245
5 0.976844 bar -0.773630 -0.570417
BTW,在我看来,以下是m矿石优雅:
在[53]:def my_test2(row):
....:return row [ 'a']%row ['c']
....:
在[54]中:df ['Value'] = df.apply(my_test2,axis = 1)
I have some problems with the Pandas apply function, when using multiple columns with the following dataframe
df = DataFrame ({'a' : np.random.randn(6),
'b' : ['foo', 'bar'] * 3,
'c' : np.random.randn(6)})
and the following function
def my_test(a, b):
return a % b
When I try to apply this function with :
df['Value'] = df.apply(lambda row: my_test(row[a], row[c]), axis=1)
I get the error message:
NameError: ("global name 'a' is not defined", u'occurred at index 0')
I do not understand this message, I defined the name properly.
I would highly appreciate any help on this issue
Update
Thanks for your help. I made indeed some syntax mistakes with the code, the index should be put ''. However I have still the same issue using a more complex function such as:
def my_test(a):
cum_diff = 0
for ix in df.index():
cum_diff = cum_diff + (a - df['a'][ix])
return cum_diff
Thank you
Seems you forgot the ''
of your string.
In [43]: df['Value'] = df.apply(lambda row: my_test(row['a'], row['c']), axis=1)
In [44]: df
Out[44]:
a b c Value
0 -1.674308 foo 0.343801 0.044698
1 -2.163236 bar -2.046438 -0.116798
2 -0.199115 foo -0.458050 -0.199115
3 0.918646 bar -0.007185 -0.001006
4 1.336830 foo 0.534292 0.268245
5 0.976844 bar -0.773630 -0.570417
BTW, in my opinion, following way is more elegant:
In [53]: def my_test2(row):
....: return row['a'] % row['c']
....:
In [54]: df['Value'] = df.apply(my_test2, axis=1)
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