Pandas - Find and index rows that match row sequence pattern

Question

I would like to find a pattern in a dataframe in a categorical variable going down rows. I can see how to use Series.shift() to look up / down and using boolean logic to fi

Answer 1

You can do this by defining a custom aggregate function, then using it in group_by statement, finally merge it back to the original dataframe. Something like this:

Aggregate function:

def pattern_detect(column):
 # define any other pattern to detect here
 p0, p1, p2, p3 = 1, 2, 2, 0       
 column.eq(p0) & \
 column.shift(-1).eq(p1) & \
 column.shift(-2).eq(p2) & \
 column.shift(-3).eq(p3)
 return column.any()

Use group by function next:

grp = df.group_by('group_var').agg([patter_detect])['row_pat']

Now merge it back to the original dataframe:

df = df.merge(grp, left_on='group_var',right_index=True, how='left')