pandas column selection code example

Example 1: select columns pandas

df1 = df.iloc[:,0:2] # Remember that Python does not slice inclusive of the ending index.

Example 2: add an index column in range dataframe

df = df.loc[df.index.repeat(df['a'])]   
df['c'] = df.groupby(level=0).cumcount() + 1
df = df.reset_index(drop=True)
print (df)
   a  b  c
0  1  x  1
1  2  y  1
2  2  y  2
3  3  z  1
4  3  z  2
5  3  z  3