Highlight duplicates in a filtered Excel Table
The image above demonstrates a conditional formatting formula applied to an Excel Table containing random data. The Excel Table has been filtered to show only records for January 2012.
There is a builtin function in Excel that lets you highlight duplicates, however, that won't work properly if you have filtered the data.
The image above shows the builtin tool highlighting duplicate items. But one item exists only once in the filtered data, however, it is highlighted as a duplicate.
The reason is that there is another item not showing in the filtered table. You need to rely on a custom conditional formatting formula if you want it to compare only filtered visible values.
Build an Excel Table
The reason I am using an Excel Table is that the conditional formatting adjusts automatically if you add or delete records. It also uses structured references so there is no need to change cell references in the formula.
The disadvantage is that you have to use the INDIRECT function each time you reference the Excel Table in the CF formula, it is not a big deal but it is worth noting.
 Select any cell in your data set.

Press short cut keys CTRL + T to open the "Create Table" dialog box.
 Enable the checkbox if the columns in the data set have header names.
 Click OK button to apply.
Create a new conditional formatting rule
 Select table column "Description".
 Go to the "Home" tab on the ribbon.
 Click the "Conditional formatting" button.
 Click "New Rule..".

Click "Use a formula to determine which cells to format".

Copy this conditional formatting formula:
=SUM(COUNTIF(INDIRECT("Table2[@Description]"), IF(SUBTOTAL(3, OFFSET(INDIRECT("Table2[Description]"), MATCH(ROW(INDIRECT("Table2[Description]")), ROW(INDIRECT("Table2[Description]")))1, 0, 1)), INDIRECT("Table2[Description]"), "")))>1
 Paste to "Format values where this formula is true:". I will explain the formula later in this article.
 Click the "Format..." button.

Go to tab "Fill".
 Pick a color.
 Click OK button.
 Click OK button again.
Explaining CF formula in cell C211
This Conditional Formatting formula highlights cells that have a duplicate in a filtered Excel Table, note that it will not be highlighted if a duplicate exists outside the filtered values (not visible).
Step 1  Create an array from 1 to n
The INDIRECT function makes it possible to use a reference to an Excel Table inside a Conditional Formatting formula. This article explains it in greater detail: How to use an Excel Table name in Data Validation Lists and Conditional Formatting formulas
The ROW function converts a cell reference to the corresponding row numbers which is useful when you want to create an array.
The MATCH function is utilized in this example to create an array that contains a sequence that begins with 1 and increments with one up to the number of values in the array.
MATCH(ROW(INDIRECT("Table2[Description]")), ROW(INDIRECT("Table2[Description]"))
becomes
MATCH(ROW(C206:C227), ROW(C206:C227))
becomes
MATCH({3; 4; ... 383; 384}, {3; 4; ... 383; 384})
and returns
{1; 2; 3; ... 380; 381}.
The Excel Table has 381 records and the size of the array matches that number.
Step 2  Modify array
This workaround makes it possible to use an array of values in a SUBTOTAL function, the OFFSET function splits the array into smaller arrays with only one value in each array.
OFFSET(reference,rows,columns,[height],[width])
It returns error values, however, the SUBTOTAL function can calculate these values anyway.
OFFSET(INDIRECT("Table2[Description]"), MATCH(ROW(INDIRECT("Table2[Description]")), ROW(INDIRECT("Table2[Description]")))1, 0, 1)
becomes
OFFSET(INDIRECT("Table2[Description]"), {1; 2; 3; ... 380; 381}1, 0, 1)
becomes
{0; 1; 2; ... ; 379; 380}
and returns
{#VALUE!; #VALUE!; #VALUE!; ... ; #VALUE!; #VALUE!}
Step 3  Identify visible values
The first argument in the SUBTOTAL function is 3 and represents the COUNTA function meaning it will count cells that are not empty.
The SUBTOTAL function will actually return an array with this setup which is very handy in this situation.
SUBTOTAL(3, OFFSET(INDIRECT("Table2[Description]"), MATCH(ROW(INDIRECT("Table2[Description]")), ROW(INDIRECT("Table2[Description]")))1, 0, 1))
becomes
SUBTOTAL(3, {#VALUE!; #VALUE!; #VALUE!; ... ; #VALUE!; #VALUE!})
and returns {0; 0; 0; ... ; 0; 0}. 0 (zero) represents a hidden value and 1 is visible.
Step 4  Create an array containing visible values
The IF function replaces 0 (zero) with nothing "" and 1 with the actual corresponding value.
IF(SUBTOTAL(3, OFFSET(INDIRECT("Table2[Description]"), MATCH(ROW(INDIRECT("Table2[Description]")), ROW(INDIRECT("Table2[Description]")))1, 0, 1)), INDIRECT("Table2[Description]"), "")
becomes
IF({0; 0; 0; ... ; 0; 0}, INDIRECT("Table2[Description]"), "")
and returns {""; ""; ""; ... ; ""; ""}.
Step 5  Check the number of times the current value exists across visible values
The COUNTIF function will return an array with this setup which we then can use to calculate a total. The reason we don't change the arguments with each other is that the range argument will not accept an array based on calculations.
COUNTIF(range, criteria)
COUNTIF(INDIRECT("Table2[@Description]"), IF(SUBTOTAL(3, OFFSET(INDIRECT("Table2[Description]"), MATCH(ROW(INDIRECT("Table2[Description]")), ROW(INDIRECT("Table2[Description]")))1, 0, 1)), INDIRECT("Table2[Description]"), ""))
becomes
COUNTIF(INDIRECT("Table2[@Description]"), {""; ""; ""; ... ; ""; ""})
becomes
COUNTIF("Chez Quiz", {""; ""; ""; ... ; ""; ""})
and returns {0; 0; 0; ... ; 0; 0}. The entire array is not shown, however, it contains a few 1's as well.
Step 6  Calculate a total
The SUM function adds all numbers in the array and returns a total.
SUM(COUNTIF(INDIRECT("Table2[@Description]"), IF(SUBTOTAL(3, OFFSET(INDIRECT("Table2[Description]"), MATCH(ROW(INDIRECT("Table2[Description]")), ROW(INDIRECT("Table2[Description]")))1, 0, 1)), INDIRECT("Table2[Description]"), "")))
becomes
SUM({0; 0; 0; ... ; 0; 0})
and returns 2.
Step 7  Check if value is larger than 1
The > larger than character is a logical operator that lets you compare values, it will return a boolean value TRUE or FALSE based on the outcome. The Conditional Formatting formula uses the boolean function to determine if the cell values should be highlighted or not.
SUM(COUNTIF(INDIRECT("Table2[@Description]"), IF(SUBTOTAL(3, OFFSET(INDIRECT("Table2[Description]"), MATCH(ROW(INDIRECT("Table2[Description]")), ROW(INDIRECT("Table2[Description]")))1, 0, 1)), INDIRECT("Table2[Description]"), "")))>1
becomes
2>1
and returns True. Cell C211 is highlighted.
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Thank you for the great post! I had spent almost a full day searching for how to highlight duplicates in a filtered list. But I have one further question. I am filtering this based on duplicate dollar amounts. How could I add in a part of the function to only highlight the duplicate amounts over $900 in the filtered table?
Oscar, Our company requires all employees to take 30 Mandatory Annual Courses. I have been tasked with streamlining the class schedule. I created in access a query that pulls all courses and personnel that are due to take these courses within 45 days. I export to excel and then sort on the courses and then the supervisor. After that I subtotal and get 30 subtotals for each course. The number of records in each subtotal course varies.
My max class size per course is 14 and the max number of people per supervisor is 5. How can I
Oscar,
My company requires all employees to take Mandatory Annual Courses.
We have 30 courses.
I have been tasked with streamlining the class schedule. I have all courses listed along with the names of the personnel along with their department and supervisor. I sort by class name and then by supervisor. I then subtotal and get 30 separate subtotals per course. Number of records in each subtotal will vary.
My max class size is 14 and the most I can pull from each supervisor per class per course is 5.
How can I create a formula for each subtotal that will determine the number of classes based on a max class size of 14 and then assign the max number of personnel per class per supervisor of 5.
Example: Course Name: Active Shooter
42 people need to attend this class, There are 6 supervisors for these 42 people. On the surface it looks like 3 classes,however one supervisor has 16 people which would exceed the max per class of 5.
Any help is appreciated.
Regards
Gene Haines
Gene Haines,
My max class size is 14 and the most I can pull from each supervisor per class per course is 5. 42 people need to attend this class, there are 6 supervisors for these 42 people.
You only have 6 supervisors, don't you need more supervisors per class per course if your class is 42? If each supervisor has 5 people you get 6x5 = 30 people.
This criteria is not met if your class is above 30 people?