Change the index of the below dataframe to the year column

7. Change the index of the below dataframe to the year column In [21]: data = { 'countrycode': ['CHN' , 'CHN' , 'CHN' , 'FRA' , 'FRA' , 'FRA' ], 'pop' : [1124.8, 1246.8, 1318.2, 58.2, 60.8, 64.7], 'rgdpe' : [2. 611, 4.951, 11. 106, 1. 294, 1. 753, 2.032], 'year' : [1990, 2000, 2010, 1990, 2000, 2010]} pwt = pd. DataFrame (data) In [23] : Out [ 23 ] : countrycode pop rgdpe year 1990 CHN 1124.8 2.611 2000 CHN 1246.8 4.951 2010 CHN 1318.2 11.106 1990 FRA 58.2 1.294 2000 FRA 60.8 1.753 2010 FRA 64.7 2.032