Removing duplicates in Power BI - Dashboard Guide

Dashboard Mode - Removing duplicates

Goal

Find unique customers from sales data by removing duplicate entries to understand how many distinct customers made purchases.

Sample Data

OrderID	Customer	Product	Amount
1001	Alice	Notebook	50
1002	Bob	Pen	5
1003	Alice	Pen	5
1004	Charlie	Notebook	50
1005	Bob	Notebook	50
1006	Diana	Pen	5

Dashboard Components

• KPI Card: Unique Customers
  Formula: Unique Customers = DISTINCTCOUNT(Sales[Customer])
  Result: 4 (Alice, Bob, Charlie, Diana)
• Matrix: Unique Customer List
  Formula: Use a matrix visual with Customer field on Rows. Power BI automatically shows unique values.
  Result: Shows Alice, Bob, Charlie, Diana once each.
• Bar Chart: Sales Amount by Customer
  Formula: SUM(Sales[Amount]) grouped by Customer
  Result: Alice=55, Bob=55, Charlie=50, Diana=5

Dashboard Layout

+----------------------+----------------------+
| Unique Customers KPI  | Unique Customer List |
|        (KPI)          |       (Matrix)       |
+----------------------+----------------------+
|           Sales Amount by Customer (Bar Chart)           |
+----------------------------------------------------------+

Interactivity

Clicking a customer name in the Unique Customer List filters the Sales Amount by Customer bar chart to show only that customer's sales. The Unique Customers KPI remains the same as it counts all distinct customers in the data.

Self Check

Add a filter for Customer = Bob. Which components update?

• The Sales Amount by Customer bar chart updates to show only Bob's sales (Amount = 55).
• The Unique Customer List updates to show only Bob.
• The Unique Customers KPI remains 4 because it counts distinct customers in the full dataset, not filtered.

Key Result

Dashboard shows unique customers count, list, and their total sales after removing duplicates.

Practice

1. What is the main purpose of removing duplicates in Power BI data?

easy

A. To add more rows to the dataset

B. To keep data clean and reliable by eliminating repeated rows

C. To change the data types of columns

D. To create new calculated columns

Solution

1. Step 1: Understand the concept of duplicates

   Duplicates are repeated rows that can cause errors or confusion in analysis.

2. Step 2: Purpose of removing duplicates

   Removing duplicates ensures the data is clean and reliable for accurate reporting.

3. Final Answer:

   To keep data clean and reliable by eliminating repeated rows -> Option B

4. Quick Check:

   Removing duplicates = Clean data [OK]

Hint: Duplicates cause errors; removing them cleans data fast [OK]

Common Mistakes:

• Thinking duplicates add useful data
• Confusing duplicates with data transformation
• Believing duplicates change data types

2. Which of the following is the correct syntax to remove duplicate rows from a table named Sales in Power Query?

easy

A. Table.RemoveDuplicates(Sales)

B. Remove.Duplicates(Sales)

C. Table.Distinct(Sales)

D. DistinctRows(Sales)

Solution

1. Step 1: Recall Power Query function for duplicates

   The correct function to remove duplicates is Table.Distinct.

2. Step 2: Apply function to the table

   Using Table.Distinct(Sales) removes duplicate rows from the Sales table.

3. Final Answer:

   Table.Distinct(Sales) -> Option C

4. Quick Check:

   Table.Distinct = Remove duplicates [OK]

Hint: Use Table.Distinct to remove duplicates in Power Query [OK]

Common Mistakes:

• Using non-existent functions like Remove.Duplicates
• Confusing syntax with other languages
• Adding extra parameters unnecessarily

3. Given the table Customers with columns CustomerID and City, what will be the result of Table.Distinct(Customers, {"CustomerID"})?

medium

A. Removes duplicate rows based on all columns

B. Removes duplicate rows based only on City column

C. Returns the original table without changes

D. Removes duplicate rows based only on CustomerID column

Solution

1. Step 1: Understand Table.Distinct with column list

   When columns are specified, duplicates are removed based on those columns only.

2. Step 2: Apply to CustomerID column

   Here, duplicates are removed based on CustomerID, ignoring other columns.

3. Final Answer:

   Removes duplicate rows based only on CustomerID column -> Option D

4. Quick Check:

   Distinct by columns = Remove duplicates by those columns [OK]

Hint: Specify columns in Table.Distinct to target duplicates [OK]

Common Mistakes:

• Assuming all columns are checked when columns are specified
• Confusing column names in the list
• Thinking it returns unchanged table

4. You wrote Table.Distinct(Sales, "ProductID") to remove duplicates by ProductID but get an error. What is the likely problem?

medium

A. The second argument should be a list of column names, not a single string

B. Table.Distinct does not accept a second argument

C. ProductID column does not exist in Sales table

D. You must use Table.RemoveDuplicates instead

Solution

1. Step 1: Check Table.Distinct syntax for columns

   The second argument must be a list of column names, e.g., {"ProductID"}, not a string.

2. Step 2: Identify error cause

   Passing "ProductID" as a string causes a syntax error because it expects a list.

3. Final Answer:

   The second argument should be a list of column names, not a single string -> Option A

4. Quick Check:

   Columns argument = List, not string [OK]

Hint: Use curly braces {} for column list in Table.Distinct [OK]

Common Mistakes:

• Passing column name as string instead of list
• Using wrong function name
• Assuming single argument works for columns

5. You have a table Orders with columns OrderID, CustomerID, and OrderDate. You want to keep only the first order per customer by date, removing duplicates of CustomerID but keeping the earliest OrderDate. Which approach is best in Power Query?

hard

A. Sort Orders by OrderDate ascending, then use Table.Distinct(Orders, {"CustomerID"})

B. Use Table.Distinct(Orders, {"CustomerID", "OrderDate"}) without sorting

C. Remove duplicates by OrderID column

D. Filter Orders to keep only rows where OrderDate is max per CustomerID

Solution

1. Step 1: Sort Orders by OrderDate ascending

   Sorting ensures earliest dates come first for each customer.

2. Step 2: Remove duplicates by CustomerID

   Using Table.Distinct(Orders, {"CustomerID"}) keeps the first row per customer, which is earliest due to sorting.

3. Final Answer:

   Sort Orders by OrderDate ascending, then use Table.Distinct(Orders, {"CustomerID"}) -> Option A

4. Quick Check:

   Sort then distinct = keep earliest per group [OK]

Hint: Sort by date first, then remove duplicates by customer [OK]

Common Mistakes:

• Removing duplicates without sorting first
• Including OrderDate in distinct columns
• Filtering by max date instead of min