Answer

To check for duplicates in a column using Conditional Formatting, apply a built-in rule that visually highlights repeated values.

Steps

1. Select the entire column containing the data.

2. Go to the Home tab.

3. Click Conditional Formatting.

4. Select Highlight Cells Rules.

5. Click Duplicate Values.

6. Choose a formatting style.

7. Click OK.

Result

Excel highlights every value that appears more than once. Highlighting updates automatically when data changes.

Windows and Mac differences

No functional difference exists. Menu names and locations remain identical.

How to check for duplicates in a column using the COUNTIF function?

To check for duplicates using a formula, use COUNTIF to count how many times each value appears.

Formula 

\text{COUNTIF(range, criteria)}

Example formula

=COUNTIF(A:A, A1)

How it works

COUNTIF returns a number greater than 1 when a value appears more than once. A return value of 1 means the value is unique.

Steps

1. Insert a new column next to the data.

2. Enter the formula in the first row of the new column.

3. Fill the formula down the column.

Interpretation

Values greater than 1 indicate duplicates.

Windows and Mac differences

No difference exists in formula behavior or syntax.

How to check for duplicates in a column using the Remove Duplicates tool?

Yes. This method identifies duplicates by removing repeated values while keeping one instance.

Steps

1. Select the column.

2. Go to the Data tab.

3. Click Remove Duplicates.

4. Confirm the selected column.

5. Click OK.

Result

Excel displays a dialog showing how many duplicate values were removed and how many unique values remain.

Data safety

Create a copy of the data before removal to preserve the original values.

Windows and Mac differences

No functional difference exists.

How to check for duplicates using Advanced Filter?

To check duplicates using Advanced Filter, extract unique records into a separate location.

Steps

1. Select the column.

2. Go to the Data tab.

3. Click Advanced.

4. Select Copy to another location.

5. Check Unique records only.

6. Choose a destination cell.

7. Click OK.

Result

Excel creates a unique list. Compare it with the original column to identify duplicates.

Windows and Mac differences

Mac displays the Advanced Filter under Data → Sort & Filter.

How to check for duplicates using PivotTable?

To check duplicates with a PivotTable, summarize how many times each value appears.

Steps

1. Select the column.

2. Go to Insert.

3. Click PivotTable.

4. Place the column in Rows.

5. Place the same column in Values.

6. Set Values to Count.

Interpretation

Counts greater than 1 represent duplicate values.

Windows and Mac differences

No functional difference exists.

How to check for duplicates in large datasets efficiently?

To check duplicates efficiently in large datasets, use COUNTIF with Conditional Formatting.

Steps

1. Select the column.

2. Open Conditional Formatting.

3. Choose New Rule.

4. Select Use a formula to determine which cells to format.

5. Enter the formula: 

   =COUNTIF(A:A, A1)>1

6. Apply formatting.

7. Click OK.

Performance

This method processes millions of cells with minimal delay when applied to a single column.

Which method is best for accuracy?

Yes. COUNTIF-based methods provide the highest accuracy because they return numeric counts for every value, allowing verification and filtering.

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