Table:
0
A
B
C
D
E
1
State (class)
Vacator
Reason for change
Successor
Date of successors formal installation
2
South Carolina (3)
Olin D. Johnston (D)
Died April 18, 1965
Donald S. Russell (D)
April 22, 1965
3
South Carolina (3)
Donald S. Russell (D)
Successor elected November 8, 1965
Ernest Hollings (D)
November 9, 1965
4
Virginia (1)
Harry F. Byrd (D)
Resigned November 10, 1965
Harry F. Byrd, Jr. (D)
November 12, 1965
5
Michigan (2)
Patrick V. McNamara (D)
Died April 30, 1966
Robert P. Griffin (R)
May 11, 1966
6
Virginia (2)
A. Willis Robertson (D)
Resigned December 30, 1966
William B. Spong, Jr. (D)
December 31, 1966

Questions and formulas:
Question: How many reasons were given when A. Willis Robertson (D) resigned?
Formula: ROWS(UNIQUE(FILTER(C1, B1="A. Willis Robertson (D)")))
Formula2: ROWS(UNIQUE(FILTER(C2:C6, B2:B6="A. Willis Robertson (D)")))
Level: medium
Question: Who vacated his post when his successor was formally installed on May 11, 1966?
Formula: UNIQUE(CHOOSECOLS(FILTER(A1:E1,E1="May 11, 1966"),2))
Formula2: UNIQUE(CHOOSECOLS(FILTER(A2:E6,E2:E6="May 11, 1966"),2))
Level: medium
Question: What was the state (class) where the new successor was formally installed on May 11, 1966?
Formula: UNIQUE(CHOOSECOLS(FILTER(A1:E1,E1="May 11, 1966"),1))
Formula2: UNIQUE(CHOOSECOLS(FILTER(A2:E6,E2:E6="May 11, 1966"),1))
Level: medium