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Question: How do I filter duplicates with a condition?

Answer:

Column B contains category and column C contains Items. Only duplicate Items with adjacent Category number 2 is listed in column E.

AA is in category 2 (row 3) and 1 but exists only once in category 2. It is not a duplicate.

BB is in category 2 and exists twice (row 4 and 9). BB has a duplicate.

CC is in category 2 and has a duplicate (row 6 and 8). CC is a duplicate.

Formula in cell E4:

If you want duplicates sorted from A to Z, read this article:

Extract a list of alphabetically sorted duplicates from a column

Learn how to filter duplicates:

Extract a list of duplicates from a column

You can also use more than one condition, this article shows you how:

Filter duplicate values using critera

Filter a unique distinct list:

5 easy ways to extract Unique Distinct Values

Explaining formula in cell E4

Step 1 - Identify values that has not been displayed before

COUNTIF($E$3:E3, $C$3:$C$9)=0

becomes

COUNTIF("Duplicate items",{"AA";"BB";"AA";"CC";"AA";"CC";"BB"})=0

and returns

{TRUE;TRUE;TRUE;TRUE;TRUE;TRUE;TRUE}

In cell E4 no values has been shown before so the array returns TRUE for all values.

How to use the COUNTIF function

Step 2 - Find duplicates in category 2

COUNTIFS($B$3:$B$9, $F$2, $C$3:$C$9, $C$3:$C$9)>1

becomes

COUNTIFS({2;2; 1;2;1; 2;2}, 2, {"AA";"BB";"AA";"CC";"AA";"CC";"BB"}, {"AA";"BB";"AA";"CC";"AA";"CC";"BB"})>1

becomes

{1;2;1;2;1;2;2}>1

and returns {FALSE;TRUE; FALSE;TRUE;FALSE; TRUE;TRUE}

How to use the COUNTIFS function

Step 3 - Multiply arrays

(COUNTIF($E$3:E3, $C$3:$C$9)=0)*(COUNTIFS($B$3:$B$9, $F$2, $C$3:$C$9, $C$3:$C$9)>1)

becomes

{TRUE;TRUE;TRUE;TRUE;TRUE;TRUE;TRUE} * {FALSE;TRUE; FALSE;TRUE;FALSE; TRUE;TRUE}

and returns {0;1; 0;1;0; 1;1}

Step 4 - Divide 1 with array

1/(((COUNTIF($E$3:E3, $C$3:$C$9)=0)*(COUNTIFS($B$3:$B$9, $F$2, $C$3:$C$9, $C$3:$C$9)>1)))

becomes

1/{0;1; 0;1;0; 1;1}

and returns {#DIV/0!; 1;#DIV/0!; 1;#DIV/0!; 1;1}

Step 5 - Find last matching value in array

The LOOKUP function ignores errors but requires the second argument to be sorted ascending. However our list contains only errors or 1 so the LOOKUP function returns the last matching 1 in the array.

LOOKUP(2, 1/(((COUNTIF($E$3:E3, $C$3:$C$9)=0)*(COUNTIFS($B$3:$B$9, $F$2, $C$3:$C$9, $C$3:$C$9)>1))), $C$3:$C$9)

becomes

LOOKUP(2, {#DIV/0!; 1;#DIV/0!; 1;#DIV/0!; 1;1}, $C$3:$C$9)

becomes

LOOKUP(2, {#DIV/0!; 1;#DIV/0!; 1;#DIV/0!; 1;1}, {"AA";"BB";"AA";"CC";"AA";"CC";"BB"})

and returns "BB" in cell E4. BB is the corresponding value to the last 1 in the array, bolded above.

How to use the LOOKUP function

Step 6 - Relative cell refences

The following cell reference is both an absolute and relative cell reference: $E$3:E3. When you copy the formula to cells below, the cell ref changes. That way the formula knows which values have been displayed before.

How to use absolute and relative references

Download excel example file

Filter duplicates with a condition.xlsx

(Excel Workbook *.xlsx)