[英]find the maximum value for each streak of numbers in another column in pandas
I have a dataframe like this : 我有一个像这样的数据框:
df = pd.DataFrame({'dir': [1,1,1,1,0,0,1,1,1,0], 'price':np.random.randint(100,200,10)})
dir price
0 1 100
1 1 150
2 1 190
3 1 194
4 0 152
5 0 151
6 1 131
7 1 168
8 1 112
9 0 193
and I want a new column that shows the maximum price as long as the dir is 1 and reset if dir is 0. My desired outcome looks like this: 并且我想要一个新列来显示最高价格,只要dir为1,并在dir为0时重置。我想要的结果如下所示:
dir price max
0 1 100 194
1 1 150 194
2 1 190 194
3 1 194 194
4 0 152 NaN
5 0 151 NaN
6 1 131 168
7 1 168 168
8 1 112 168
9 0 193 NaN
Use transform
with max
for filtered rows: transform
max
transform
用于已过滤的行:
#get unique groups for consecutive values
g = df['dir'].ne(df['dir'].shift()).cumsum()
#filter only 1
m = df['dir'] == 1
df['max'] = df[m].groupby(g)['price'].transform('max')
print (df)
dir price max
0 1 100 194.0
1 1 150 194.0
2 1 190 194.0
3 1 194 194.0
4 0 152 NaN
5 0 151 NaN
6 1 131 168.0
7 1 168 168.0
8 1 112 168.0
9 0 193 NaN
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