Removing duplicates in Power BI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'removing duplicates' mean in Power BI?

It means deleting repeated rows in your data so each record is unique. This helps keep your reports clean and accurate.

beginner

Which Power BI tool is commonly used to remove duplicates?

Power Query Editor is used to remove duplicates by selecting columns and choosing 'Remove Duplicates'.

beginner

How do you remove duplicates from a specific column in Power Query?

Select the column, then click 'Remove Duplicates' in the Home tab. Only unique values in that column remain.

intermediate

What happens if you remove duplicates based on multiple columns?

Power BI keeps rows unique across all selected columns combined, removing rows where all those columns match another row.

intermediate

Can you remove duplicates using DAX in Power BI?

DAX does not remove duplicates from tables directly but you can create calculated tables or measures that summarize unique values.

Which Power BI feature is best for removing duplicate rows?

A Data View

B DAX Measures

C Power Query Editor

D Report View

Power Query Editor is designed for data transformation tasks like removing duplicates.

What does 'Remove Duplicates' do when applied to one column in Power Query?

A Deletes all rows with repeated values in that column

B Keeps only one row for each unique value in that column

C Deletes the column

D Sorts the column alphabetically

It keeps one row per unique value, removing extra rows with the same value.

If you select multiple columns and remove duplicates, what is the result?

A Rows with duplicate values in any one column are removed

B Only the first column is checked for duplicates

C Duplicates are highlighted but not removed

D Rows are removed only if all selected columns have duplicate values

Duplicates are removed only when all selected columns match another row.

Can you remove duplicates directly in a DAX measure?

A No, DAX can only create calculations or filtered views

B Yes, DAX can delete rows

C Yes, but only for numeric columns

D No, DAX is only for visuals

DAX cannot delete rows but can create tables or measures that show unique values.

Why is removing duplicates important in Power BI?

A To ensure data accuracy and avoid double counting

B To reduce file size only

C To change data types

D To create new columns

Removing duplicates helps keep data accurate and prevents errors in analysis.

Explain how to remove duplicates from a dataset in Power BI using Power Query.

Think about the steps you take to clean data before analysis.

Describe the difference between removing duplicates in Power Query and handling duplicates with DAX.

Consider the roles of Power Query and DAX in Power BI.

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