Duplicate row and add a column pandas-CodePudding

I need to duplicate each row 3 times and add two new columns. The new column values are different for each row.

import pandas as pd
df = {'A': [ 8,9,12],
      'B': [ 1,11,3],
      'C': [ 7,9,13],
      'D': [81,92,121]}
df = pd.DataFrame(df)
#####################################################
      #input
   A    B      C     D
   8    1      7    81  
   9    11     9    92 
  12    3     13   121 
 ####################################################
#expected output
   A    B      C     D    E    F
   8    1      7    81    9    8   E=A 1,  F= C 1
   8    1      7    81    8    7   E=A,    F= C
   8    1      7    81    7    6   E=A-1,  F= C-1
   9    11     9    92    10   10
   9    11     9    92    9    9
   9    11     9    92    8    8  
  12    3     13   121    13  14
  12    3     13   121    12  13
  12    3     13   121    11  12

CodePudding user response：

To repeat the DataFrame you can use np.repeat(). Afterwards you can create a list to add to "A" and "C".

df = pd.DataFrame(np.repeat(df.to_numpy(), 3, axis=0), columns=df.columns)
extra = [1,0, -1]*3
df['E'] = df['A'] extra
df['F'] = df['C'] extra

This gives:

    A   B   C    D   E   F
0   8   1   7   81   9   8
1   8   1   7   81   8   7
2   8   1   7   81   7   6
3   9  11   9   92  10  10
4   9  11   9   92   9   9
5   9  11   9   92   8   8
6  12   3  13  121  13  14
7  12   3  13  121  12  13
8  12   3  13  121  11  12

CodePudding user response：

Use Index.repeat with DataFrame.loc for repeat rows, then repeat integers [1,0,-1] by numpy.tile and create new columns E, F:

df1 = df.loc[df.index.repeat(3)]

g = np.tile([1,0,-1], len(df))
df1[['E','F']] = df1[['A','C']].add(g, axis=0).to_numpy()
df1 = df1.reset_index(drop=True)
print (df1)
    A   B   C    D   E   F
0   8   1   7   81   9   8
1   8   1   7   81   8   7
2   8   1   7   81   7   6
3   9  11   9   92  10  10
4   9  11   9   92   9   9
5   9  11   9   92   8   8
6  12   3  13  121  13  14
7  12   3  13  121  12  13
8  12   3  13  121  11  12