group and modify rows by index python pandas-CodePudding

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?

CodePudding user response：

I'm not sure if this is the most efficient way of solving this, but the given code works:

    import pandas as pd

    alist = []
    
    for i in range(0,1000):
       alist.append(2)
  
    data = {'a':alist}
    dataset = pd.DataFrame(data)

    count = 2

    for i in range(0, (len(alist)//3), 3):
       dataset.iloc[i: i 3 ] = count
       count = count   1

I have looped through the dataframe a third of the total times while increasing the loop count by 3 and at every position used iloc to replace the value of the given column of the current row as well as the 2 after it with a variable count which was initialized from 2 and incremented at each step.

CodePudding user response：

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)