state (class)                                        vacator                                reason for change                  successor date of successors formal installation
0        virginia (1)                                         vacant                                 failure to elect  isaac s pennybacker ( d )              elected december 3 , 1845
1   massachusetts (2)                            isaac c bates ( w )                             died march 16 , 1845           john davis ( w )                elected march 24 , 1845
2   new hampshire (2)                        benning w jenness ( d )  resigned june 13 , 1846 after successor elected        joseph cilley ( d )                 elected june 13 , 1846
3  south carolina (3)                          george mcduffie ( d )                        resigned august 17 , 1846        andrew butler ( d )              elected december 4 , 1846
4            iowa (2)  iowa admitted to the union december 28 , 1846    iowa admitted to the union december 28 , 1846                     vacant                   not filled this term
5            iowa (3)  iowa admitted to the union december 28 , 1846    iowa admitted to the union december 28 , 1846                     vacant                   not filled this term
6       louisiana (2)                         alexander barrow ( w )                          died december 29 , 1846         pierre soulã ( d )              elected january 21 , 1847

Table as JSON:
{"state (class)":{"0":"virginia (1)","1":"massachusetts (2)","2":"new hampshire (2)","3":"south carolina (3)","4":"iowa (2)","5":"iowa (3)","6":"louisiana (2)"},"vacator":{"0":"vacant","1":"isaac c bates ( w )","2":"benning w jenness ( d )","3":"george mcduffie ( d )","4":"iowa admitted to the union december 28 , 1846","5":"iowa admitted to the union december 28 , 1846","6":"alexander barrow ( w )"},"reason for change":{"0":"failure to elect","1":"died march 16 , 1845","2":"resigned june 13 , 1846 after successor elected","3":"resigned august 17 , 1846","4":"iowa admitted to the union december 28 , 1846","5":"iowa admitted to the union december 28 , 1846","6":"died december 29 , 1846"},"successor":{"0":"isaac s pennybacker ( d )","1":"john davis ( w )","2":"joseph cilley ( d )","3":"andrew butler ( d )","4":"vacant","5":"vacant","6":"pierre soulã ( d )"},"date of successors formal installation":{"0":"elected december 3 , 1845","1":"elected march 24 , 1845","2":"elected june 13 , 1846","3":"elected december 4 , 1846","4":"not filled this term","5":"not filled this term","6":"elected january 21 , 1847"}}