Pandas DataFrame set consecutive values to nan until value in column changes-CodePudding

I have the following DataFrame, where Value refers to my observations, and Criterion indicates, when a Value should be set to np.nan.

Value	Criterion
3	0
3	0
5	1
7	0
2	0
2	0
8	1
8	0
8	0
1	0

Whenever Criterion is equal to 1, I want to set the Value in the same row, as well as all consecutive Values to zero until Value changes. The desired output should look like this.

Value	Criterion
3	0
3	0
nan	1
7	0
2	0
2	0
nan	1
nan	0
nan	0
1	0

CodePudding user response：

Create groups by consecutive values in Value column and test if at least one 1 in Criterion, then set NaN per group in Series.mask:

s = df['Value'].ne(df['Value'].shift()).cumsum()

df['Value'] = df['Value'].mask(df['Criterion'].groupby(s).transform('any'))
print (df)
   Value  Criterion
0    3.0          0
1    3.0          0
2    NaN          1
3    7.0          0
4    2.0          0
5    2.0          0
6    NaN          1
7    NaN          0
8    NaN          0
9    1.0          0

Or if need test first value is 1 per consecutive groups in column Criterion use:

s= df['Value'].ne(df['Value'].shift()).cumsum()

df['Value'] = df['Value'].mask(df['Criterion'].groupby(s).transform('first').eq(1))