column_changes

import pandas as pd
import numpy as np
np.random.seed(5)
df = pd.DataFrame(np.random.randint(100, size=(100, 6)),
                  columns=list('ABCDEF'),
                  index=['R{}'.format(i) for i in range(100)])

print(df.head())

     A   B   C   D   E   F
R0  99  78  61  16  73   8
R1  62  27  30  80   7  76
R2  15  53  80  27  44  77
R3  75  65  47  30  84  86
R4  18   9  41  62   1  82



print(df.loc['R2':'R4', 'C':'D'])



# get the list if index for a < 50

con=df[df['A']<50].index.tolist()




# add new column -- big but for the index above --small

df['new'] = 'big'

df['new'][df.index.isin(con)] = 'small'


print(df)


#      A   B   C   D   E   F    new
R0   99  78  61  16  73   8    big
R1   62  27  30  80   7  76    big
R2   15  53  80  27  44  77  small
R3   75  65  47  30  84  86    big
R4   18   9  41  62   1  82  small
..   ..  ..  ..  ..  ..  ..    ...
R95  19   7  76  66  56   0  small
R96  57  31  86  74  37  64    big
R97  51  12  59  25  39  33    big
R98  24   7  68  81  69  69  small
R99  81  20  86   1  74  70    big