How would you figure out an unique list where the sum of in one column doesn't match the other column? I'm comparing list 1 to list 2
List 1
A 10
A 10
B 5
B 6
B 4
List 2
A 10
A 10
B 5
B 6

Array formula in cell B10:

=INDEX(\$E\$3:\$E\$7, MATCH(0, COUNTIFS(\$B\$3:\$B\$7, \$E\$3:\$E\$7, \$C\$3:\$C\$7, \$F\$3:\$F\$7) + COUNTIF(\$B\$9:B9, \$E\$3:\$E\$7), 0))

### How to enter an array formula

1. Select cell B10
2. Type the above formula
3. Press and hold CTRL + SHIFT simultaneously
4. Press Enter once
5. Release all keys

If you did it right, the formula is now encapsulated with curly brackets, like this: {formula}

Don´t enter these characters yourself, they show up automatically.

### Explaining the array formula in cell B10

Step 1 - Compare lists

The COUNTIFS function compares column by column between the two lists. If a record is found 1 or more is returned. Nothing found 0 is returned.

COUNTIFS(\$B\$3:\$B\$7, \$E\$3:\$E\$7, \$C\$3:\$C\$7, \$F\$3:\$F\$7)

returns

{ 1; 1; 1; 1; 0}

Step 2 - Filter only unique distinct values

The COUNTIF function makes sure that only unique distinct values are returned. If a value already exists in the list the function returns 1.

The first argument has a relative and absolute cell reference \$B\$9:B9. The cell reference expands as you copy and paste the formula further down.

COUNTIF(\$B\$9:B9, \$E\$3:\$E\$7)

returns

{0; 0; 0; 0; 0}

This means that no values have been shown yet.

Step 3 - Find the relative position

The MATCH function finds the relative position of the first 0 in the array.

MATCH(0, COUNTIFS(\$B\$3:\$B\$7, \$E\$3:\$E\$7, \$C\$3:\$C\$7, \$F\$3:\$F\$7) + COUNTIF(\$B\$9:B9, \$E\$3:\$E\$7), 0)

becomes

MATCH(0, { 1; 1; 1; 1; 0} + {0; 0; 0; 0; 0}, 0)

becomes

MATCH(0, { 1; 1; 1; 1; 0} , 0)

and returns 5.

Step 3 - Return values

The INDEX function returns a value in a cell range.

INDEX(\$E\$3:\$E\$7, 5)

becomes

INDEX({"A"; "A"; "B"; "B"; "B"}, 5)

and returns B in cell B10.