

In [1]:

    
import pandas as pd



In [2]:

    
pd.__version__









    Out[2]:





'0.24.2'

loc

locate by label



In [157]:

    
df_default_index = pd.DataFrame({
    'name':['john','mary','peter','nancy','gary'],
    'age':[22,33,27,22,31],
    'state':['AK','DC','CA','CA','NY']
})
df_default_index



In [158]:

    
df_default_index.loc[[0]]



In [159]:

    
df_default_index.loc[[2,3]]



In [130]:

    
df_name_index = pd.DataFrame(
    index=['john','mary','peter','nancy','gary'],
    data={
        'age':[22,33,27,22,31],
        'state':['AK','DC','CA','CA','NY']
    }
)



In [131]:

    
df_name_index



In [133]:

    
df_name_index.loc[['peter']]









    Out[133]:







  
    
      
      age
      state
    
  
  
    
      peter
      27
      CA



In [143]:

    
df_name_index.loc[['john']]

iloc

locate by position



In [134]:

    
df_name_index.iloc[[0]]



In [141]:

    
df_name_index.iloc[[2,3,4]]



In [135]:

    
df_default_index.iloc[[0]]



In [142]:

    
df_default_index.iloc[[2,3,4]]

set value to individual cell

must use loc



In [155]:

    
df_set = pd.DataFrame({
    'name':['john','mary','peter','nancy','gary'],
    'age':[22,33,27,22,31],
    'state':['AK','DC','CA','CA','NY']
})
df_set



In [156]:

    
df_set.loc[0,'name'] = 'bartholomew'

df_set.loc[3, 'age'] = 39

df_set









    Out[156]:







  
    
      
      name
      age
      state
    
  
  
    
      0
      bartholomew
      22
      AK
    
    
      1
      mary
      33
      DC
    
    
      2
      peter
      27
      CA
    
    
      3
      nancy
      39
      CA
    
    
      4
      gary
      31
      NY



In [148]:

    
df_name_index.loc['john','age'] = 99
df_name_index

settingwithcopywarning

bad:



In [53]:

    
df_over_30_years = df[df['age']>30]
df_over_30_years



In [54]:

    
df_over_30_years['new_column'] = 'some_value'









    



/home/felipe/venv36/lib/python3.6/site-packages/ipykernel_launcher.py:1: SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead

See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
  """Entry point for launching an IPython kernel.

good:



In [49]:

    
df_over_30_years = df.copy()[df['age']>30]
df_over_30_years



In [50]:

    
df_over_30_years['new_column'] = 'some_value'



In [51]:

    
df_over_30_years









    Out[51]:







  
    
      
      name
      age
      state
      new_column
    
  
  
    
      1
      mary
      33
      DC
      some_value
    
    
      4
      gary
      31
      NY
      some_value