group and modify rows by index python pandas

Question

I have a question on pandas-python: Say I have a column with 1000+ elements (integers), and its name is 'a' like

'a' = [2,2,2,2,2,2,2,2,2,2,2,2,..............]

I want to modify the elements by row index(every third number increase by 1 till the end of the column), and deleting the name. My final (and desired) output wold be:

'b' = [2,2,2,3,3,3,4,4,4,5,5,5..................]

Any hint?

Answer 1

a = [2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2]
c = []
for i in range(0, len(a), 3):
    b = a[i : i + 3]
    for j in range(len(b)):
        b[j] = b[j] + (i // 3)
    c.extend(b)
print(c)