为什么我的Pandas“apply”函数引用了多个列却不起作用呢？[关闭]

Question

Pandas apply函数有一些问题，当使用以下数据帧的多列时

df = DataFrame ({'a' : np.random.randn(6),
                 'b' : ['foo', 'bar'] * 3,
                 'c' : np.random.randn(6)})

def my_test(a, b):
    return a % b

df['Value'] = df.apply(lambda row: my_test(row[a], row[c]), axis=1)

NameError: ("global name 'a' is not defined", u'occurred at index 0')

def my_test(a):
    cum_diff = 0
    for ix in df.index():
        cum_diff = cum_diff + (a - df['a'][ix])
    return cum_diff 

Answer 1

似乎您忘记了字符串的''。

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

顺便说一句，在我看来，下面的方式更优雅：

In [53]: def my_test2(row):
....:     return row['a'] % row['c']
....:     

In [54]: df['Value'] = df.apply(my_test2, axis=1)