Table:
0
A
B
C
D
E
1
State (class)
Vacator
Reason for change
Successor
Date of successors formal installation
2
Virginia (1)
Vacant
Virginia re-admitted to the Union
John F. Lewis (R)
January 26, 1870
3
Virginia (2)
Vacant
Virginia re-admitted to the Union
John W. Johnston (D)
January 26, 1870
4
Mississippi (1)
Vacant
Mississippi re-admitted to the Union
Adelbert Ames (R)
February 23, 1870
5
Mississippi (2)
Vacant
Mississippi re-admitted to the Union
Hiram R Revels (R)
February 23, 1870
6
Texas (1)
Vacant
Texas re-admitted to the Union
James W. Flanagan (R)
March 30, 1870
7
Texas (2)
Vacant
Texas re-admitted to the Union
Morgan C. Hamilton (R)
March 31, 1870
8
Georgia (3)
Vacant
Georgia re-admitted to the Union
Joshua Hill (R)
February 1, 1871
9
Georgia (2)
Vacant
Georgia re-admitted to the Union
Homer V. M. Miller (D)
February 28, 1871
10
Maine (2)
William P. Fessenden (R)
Died September 8, 1869
Lot M. Morrill (R)
October 30, 1869
11
Minnesota (2)
Daniel S. Norton (R)
Died July 13, 1870
William Windom (R)
July 15, 1870
12
Missouri (3)
Daniel T. Jewett (R)
Successor elected January 20, 1871
Francis P. Blair, Jr. (D)
January 20, 1871

Questions and formulas:
Question: Who were the successors when the date the successors were installed was February 23, 1870?
Formula: UNIQUE(CHOOSECOLS(FILTER(A1:E1,E1="February 23, 1870"),4))
Formula2: UNIQUE(CHOOSECOLS(FILTER(A2:E12,E2:E12="February 23, 1870"),4))
Level: medium
Question: Who was the vacator when the successor was formally installed on February 1, 1871?
Formula: UNIQUE(CHOOSECOLS(FILTER(A1:E1,E1="February 1, 1871"),2))
Formula2: UNIQUE(CHOOSECOLS(FILTER(A2:E12,E2:E12="February 1, 1871"),2))
Level: medium
Question: Who was the successor that was formally installed on March 30, 1870?
Formula: UNIQUE(CHOOSECOLS(FILTER(A1:E1,E1="March 30, 1870"),4))
Formula2: UNIQUE(CHOOSECOLS(FILTER(A2:E12,E2:E12="March 30, 1870"),4))
Level: medium