python - 不同列的比较顺序，并根据比较将字符串添加到新列

Question

将一对列和结果作为枚举与新列进行比较，并比较另一对列并将结果作为枚举与同一新列进行比较

df如图:

a   b   c   d   length
18  32  76  75  8
64  63  76  64  9
55  84  98  45  0
72  92  87  65  0
76  83  23  56  0
36  87  97  12  11

如虚拟数据框中所示，我正在按顺序比较列

1. 如果 b > a 则过滤
2. 如果 d > c 则过滤
3. 如果长度为0则过滤

我的代码如下，

df['status_flag'] = np.where(df['b']>=df['a'], "Filtered out based on b>a", None)
df['status_flag'] = np.where(df['d']>=df['c'], "Filtered out based on b>a", None)
df['status_flag'] = np.where(df['e']==0, "Filtered out based on length", None)

此产量输出为:

a   b   c   d   length      new
18  32  76  75  8       
64  68  76  94  9       
55  84  98  99  0       "Filtered out based on length"
72  92  87  65  0       
76  83  23  56  0       "Filtered out based on length"
36  87  97  100 11

基本上它用 None 替换现有字符串。如何以不同的方式做到这一点。

预期输出:

a   b   c   d   length      new
18  32  76  75  8       "Filtered out based on b>a"
64  68  76  94  9       "Filtered out based on d>c"
55  84  98  99  0       "Filtered out based on length"
72  92  87  65  0       "Filtered out based on d>c"
76  83  23  56  0       "Filtered out based on length"
36  87  97  100 11      "Passed all filters"

Answer 1

您可以通过以下方式完成此操作:

# Apply filters in the reverse order to get the sequence you want
df['new'] = 'Passed all filters'
df.loc[df.b > df.a, 'new'] = 'Filtered out based on b>a'
df.loc[df.d > df.c, 'new'] = 'Filtered out based on d>c'
df.loc[df.length == 0, 'new'] = 'Filtered out based on length'
print(df)

    a   b   c   d  length                           new
0  18  32  76  75       8     Filtered out based on b>a
1  64  63  76  64       9            Passed all filters
2  55  84  98  45       0  Filtered out based on length
3  72  92  87  65       0  Filtered out based on length
4  76  83  23  56       0  Filtered out based on length
5  36  87  97  12      11     Filtered out based on b>a

注意:这使用给定的第一个数据帧，该数据帧与示例中使用的数据帧不同。使用该结果会产生以下结果:

    a   b   c    d  length                           new
0  18  32  76   75       8     Filtered out based on b>a
1  64  68  76   94       9     Filtered out based on d>c
2  55  84  98   99       0  Filtered out based on length
3  72  92  87   65       0  Filtered out based on length
4  76  83  23   56       0  Filtered out based on length
5  36  87  97  100      11     Filtered out based on d>c