Dax Function: COMBIN

Category: Statistical Functions

The COMBIN function in Power BI calculates the number of combinations for a given number of items, taking a specified number of items at a time. A combination is a selection of items where the order does not matter.

Purpose 

To compute how many ways items can be selected from a set without considering the order.

Type of Calculations

 Combinatorial mathematics.

Practical Use Cases

  • Analyzing scenarios in probability and statistics.
  • Solving problems related to grouping or selecting subsets, such as team formation or lottery odds.
  • Useful in business scenarios like product bundling, resource allocation, and market segmentation analysis.

COMBIN(number, number_chosen)
ParameterTypeDescription
numberScalarThe total number of items. Must be greater than or equal to number_chosen.
number_chosenScalarThe number of items to select at a time. Must be a non-negative integer.

How Does COMBIN Dax Works

The formula used by the COMBIN function is:

Where:

  • n is the total number of items (number).

  • r is the number of items chosen at a time (number_chosen).

  • n! denotes the factorial of nn, which is the product of all positive integers up to nn.

Example Calculation

For COMBIN(5, 2):

What Does It Return?

The function returns an integer value:

  • Represents the total number of combinations possible when selecting number_chosen items from a set of number items.

  • The value is always non-negative.

When Should We Use It?

  • To solve problems where order does not matter (e.g., selecting a committee).

  • In probability calculations to find the total number of outcomes for an event.

  • To evaluate business scenarios involving grouping or bundling without considering sequence.

Examples

Basic Usage :

Calculate the number of ways to choose 3 items from a set of 7:


COMBIN(7, 3)

Output: 35

Column Usage

Apply the function to calculate combinations dynamically for data in a column:


COMBIN(Table[TotalItems], Table[ChosenItems])

This computes combinations for each row based on the values in TotalItems and ChosenItems.

Advanced Usage

Combine COMBIN with other DAX functions for conditional calculations:


IF(COMBIN(10, 4) > 20, "Many Combinations", "Few Combinations")

This evaluates whether the number of combinations exceeds a threshold and returns a corresponding label.

Tips and Tricks

  • Integer Inputs: Ensure number and number_chosen are integers to avoid errors.

  • Performance: Pre-compute combinations for large datasets or frequently used values to optimize performance.

  • Zero Handling: COMBIN(n, 0) always returns 1, as there is exactly one way to select nothing.

Potential Pitfalls

  • Constraints: The value of number_chosen must not exceed number.

  • Factorial Limits: Extremely large values of number can lead to computational limits due to factorial calculations.

Performance Impact of COMBIN DAX Function:

  • Efficient for small to medium datasets.

  • For large datasets, factorial calculations might become computationally expensive. Consider optimizations or alternative methods for approximation.

Related Functions You Might Need

  • PERMUT: Calculates permutations where the order of selection matters.

  • FACT: Computes the factorial of a number.

  • COUNTROWS: Counts the number of rows, useful for calculating the total number of items dynamically.

Want to Learn More?
For more information, check out the official Microsoft documentation for COMBIN You can also experiment with this function in your Power BI reports to explore its capabilities.

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1. What does the COMBIN function do?

It calculates the number of ways to choose a subset of items from a larger set without considering order.

2. What is the difference between COMBIN and PERMUT?

COMBIN ignores order in selection, while PERMUT considers order.

3. What happens if number_chosen is greater than number?

The function will return an error since it is impossible to select more items than available.

4. Can COMBIN handle fractional inputs?

No, both number and number_chosen must be integers.

5. How is COMBIN used in real-world scenarios?

It is used in statistics, business modeling, and probability to calculate grouping possibilities.

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