python - 根据多个条件比较数据帧的一行

Question

我的数据框是这样的:

    price        trend  decreasing  increasing  condition_decreasing
    0   7610.4  no trend    0.0     False       
    1   7610.4  no trend    0.0     False       
    2   7610.4  no trend    0.0     False       
    3   7610.4  decreasing  7610.4  True        
    4   7610.4  decreasing  7610.4  False       
    5   7610.4  decreasing  7610.4  False       
    6   7610.4  decreasing  7610.4  False       
    7   7610.4  decreasing  7610.4  False       
    8   7610.4  decreasing  7610.4  False       
    9   7610.4  decreasing  7610.4  False       
    10  7610.3  no trend    0.0     True        
    11  7610.3  no trend    0.0     False       
    12  7613.9  no trend    0.0     False   
    13  7613.9  no trend    0.0     False
    14  7613.4  no trend    0.0     False
    15  7613    decreasing  7613    True    
    16  7612    decreasing  7612    False 
    17  7612    decreasing  7612    False
    18  7612    no trend    7612    True

我基本上需要做的是，当 trend 列从 no trend 变为 decreasing 时，从 列中获取该值code>price 并将其与 price 列趋势从 decreasing 变为 no trend 时的列值进行比较。因此，在上面的示例中，它将比较第 3 行的值 7610.4 和第 10 行的值 7610.3。

我尝试添加一个列来指示列趋势何时发生变化，使用以下代码:condition_decreasing = (data['trend'] != data['trend'].shift(1))

但是在我不知道如何在循环中迭代数据框并比较两个价格之后......有什么想法吗？感谢您的帮助!

预期的输出将是这样的数据框:

price    trend  decreasing  increasing  condition_decreasing output
0   7610.4  no trend    0.0     False       
1   7610.4  no trend    0.0     False       
2   7610.4  no trend    0.0     False       
3   7610.4  decreasing  7610.4  True        
4   7610.4  decreasing  7610.4  False       
5   7610.4  decreasing  7610.4  False       
6   7610.4  decreasing  7610.4  False       
7   7610.4  decreasing  7610.4  False       
8   7610.4  decreasing  7610.4  False       
9   7610.4  decreasing  7610.4  False       
10  7610.3  no trend    0.0     True        -0.1
11  7610.3  no trend    0.0     False       
12  7613.9  no trend    0.0     False 
13  7613.9  no trend    0.0     False
14  7613.4  no trend    0.0     False
15  7613    decreasing  7613    True    
16  7612    decreasing  7612    False 
17  7612    decreasing  7612    False
18  7612    no trend    7612    True        -1

所以基本上是包含两个价格差的列 7610.3 - 7610.4

Answer 1

我们可以使用DataFrame.reindex计算差异后:

m=data['trend'].ne( data['trend'].shift()
                                 .fillna(data['trend']) )
data['output']=( data.loc[m,'price'].diff()
                     .reindex(data.index)
                     .where(data['trend'].eq('no trend')) )
                    #.where(data['trend'].ne('decreasing'))  )
                    #.where(data['trend'].str.replace(' ','').eq('notrend')) )

print(data)

# m is your condition_decreasing column

#data['output']=( data.loc[data['condition_decreasing'],'price']
#                     .diff()
#                     .reindex(data.index)
#                     .where(data['trend'].eq('no trend')) )

输出

     price            trend  decreasing_increasing  output
0   7610.4         no trend                    0.0     NaN
1   7610.4         no trend                    0.0     NaN
2   7610.4         no trend                    0.0     NaN
3   7610.4       decreasing                 7610.4     NaN
4   7610.4       decreasing                 7610.4     NaN
5   7610.4       decreasing                 7610.4     NaN
6   7610.4       decreasing                 7610.4     NaN
7   7610.4       decreasing                 7610.4     NaN
8   7610.4       decreasing                 7610.4     NaN
9   7610.4       decreasing                 7610.4     NaN
10  7610.3         no trend                    0.0    -0.1
11  7610.3         no trend                    0.0     NaN
12  7613.9         no trend                    0.0     NaN