Table:
0
A
B
C
D
E
1
State (class)
Vacator
Reason for change
Successor
Date of successors formal installation
2
Delaware (1)
George R. Riddle (D)
Died March 29, 1867
James A. Bayard, Jr. (D)
April 5, 1867
3
Arkansas (2)
Vacant
Arkansas re-admitted to the Union
Alexander McDonald (R)
June 22, 1868
4
Arkansas (3)
Vacant
Arkansas re-admitted to the Union
Benjamin F. Rice (R)
June 23, 1868
5
Florida (3)
Vacant
Florida re-admitted to the Union
Thomas W. Osborn (R)
June 25, 1868
6
Louisiana (2)
Vacant
Louisiana re-admitted to the Union
John S. Harris (R)
July 8, 1868
7
Louisiana (3)
Vacant
Louisiana re-admitted to the Union
William P. Kellogg (R)
July 9, 1868
8
Alabama (2)
Vacant
Alabama re-admitted to the Union
Willard Warner (R)
July 13, 1868
9
Alabama (3)
Vacant
Alabama re-admitted to the Union
George E. Spencer (R)
July 13, 1868
10
Maryland (1)
Reverdy Johnson (D)
Resigned July 10, 1868
William P. Whyte (D)
July 13, 1868
11
North Carolina (2)
Vacant
North Carolina re-admitted to the Union
Joseph C. Abbott (R)
July 14, 1868
12
North Carolina (3)
Vacant
North Carolina re-admitted to the Union
John Pool (R)
July 14, 1868
13
South Carolina (2)
Vacant
South Carolina re-admitted to the Union
Thomas J. Robertson (R)
July 15, 1868
14
South Carolina (3)
Vacant
South Carolina re-admitted to the Union
Frederick A. Sawyer (R)
July 16, 1868

Questions and formulas:
Question: List the number of vacators when successors were formally installed on June 22, 1868.
Formula: UNIQUE(CHOOSECOLS(FILTER(A1:E1,E1="June 22, 1868"),2))
Formula2: UNIQUE(CHOOSECOLS(FILTER(A2:E14,E2:E14="June 22, 1868"),2))
Level: medium
Question: List all state classes when successors were formally installed on June 22, 1868.
Formula: UNIQUE(CHOOSECOLS(FILTER(A1:E1,E1="June 22, 1868"),1))
Formula2: UNIQUE(CHOOSECOLS(FILTER(A2:E14,E2:E14="June 22, 1868"),1))
Level: medium