Rolling Record Of First Time Changes (& Diffs) Between Two Columns In A Df

My data is stored in a pandas dataframe. Rule: _Store the first value that appears in either col1 or col2. (Here it's df['col2'][0]). _ Increment the row, if the next number appea

Solution 1:

This might be of help

df['col'] = np.where(df.col1.isnull(), 'col2', 'col1')

df['group'] = (df.col != df.col.shift(1)).astype('int').cumsum()

df['value'] = np.where(df.col1.isnull(), df['col2'], df['col1'])

df['first'] = df.value.groupby(df.group).transform(lambda s: s.iget(0))

df
       col1     col2   col  group    value    first
0       NaN  46.8400  col2      1  46.8400  46.8400
1       NaN  46.8400  col2      1  46.8400  46.8400
2       NaN  46.8400  col2      1  46.8400  46.8400
3       NaN  46.8400  col2      1  46.8400  46.8400
4   44.9501      NaN  col1      2  44.9501  44.9501
5   44.9731      NaN  col1      2  44.9731  44.9501
6   45.0229      NaN  col1      2  45.0229  44.9501
7   45.0480      NaN  col1      2  45.0480  44.9501
8   45.0753      NaN  col1      2  45.0753  44.9501
9       NaN  45.0753  col2      3  45.0753  45.0753
10      NaN  45.0753  col2      3  45.0753  45.0753

df['first'].diff(1).groupby(df.group).first()
group
1           NaN
2       -1.8899
3        0.1252