pandas DataFrame index (the difference between iloc and loc)

Pandas - the difference between ix vs loc vs iloc

0. DataFrame

• The construction of DataFrame mainly depends on the following three parameters:

  • data: table data;
  • index: row index;
  • columns: column name;
    
    • index indexes rows, and columns indexes columns;

  import pandas as pd  
  data = [[1,2,3],[4,5,6]]  
  index = [0,1]  
  columns=['a','b','c']  
  df = pd.DataFrame(data=data, index=index, columns=columns)  

1. loc

• iloc gets a row by row index:

  >> df.loc[1]
  a    4 
  b    5 
  c    6 

• If the DataFrame is constructed with indices not integers but characters:

  index = ['d','e']  
  columns=['a','b','c'] 
  df = pd.DataFrame(data=data, index=index, columns=columns)
  
  >> df.loc['d']

• Index a column:

  >> df.loc['d', ['b', 'c']]  
  >> df.loc[:, ['c']] 

2. iloc

Different from loc, iloc indexes rows by row number, and an error is reported by row index:

• df.iloc[0:] : index all rows;
• df.iloc[:, [1]] : index the first column