I want to consider a window of size 3, in which I take the last value from the b column, and the other 2 values from the a column, like in this example:
df = pd.DataFrame.from_dict({'a':[1, 2, 3, 4, 5], 'b':[10, 20, 30, 40, 50]})
df['hybrid_mean_3'] = [10, 10.5, 11, 15, 19] # how do I calculate this?
a b c
0 1 10 10.0
1 2 20 10.5 # (20+1) / 2
2 3 30 11.0 # (30+2+1) / 3
3 4 40 15.0 # (40+3+2) / 3
4 5 50 19.0 # (50+4+3) / 3
Using a rolling calculation :
N = 3
roll = df["a"].rolling(N-1, closed="left", min_periods=1)
df["c"] = (roll.sum().add(df["b"]) / roll.count().add(1)).combine_first(df["b"])
Output :
a b c
0 1 10 10.0
1 2 20 10.5
2 3 30 11.0
3 4 40 15.0
4 5 50 19.0