# Power Pivot Principles: The A to Z of DAX Functions – COMBINA

17 May 2022

*In our long-established Power Pivot Principles articles, we continue our series on the A to Z of Data Analysis eXpression (DAX) functions. This week, we look at COMBINA.*

*The COMBINA function*

This function returns the number of combinations (with repetitions) for a given number of items. If this sounds a little confusing, think of it this way: you have a **number **of balls in the bag, each with a different number on it. You take one ball out at random, record its number, then replace it. You do this **number_chosen** times. Ignoring the sequence of the numbers selected, **COMBINA** deduces the number of different combinations. Since there is replacement, **number_chosen** may exceed the **number** too.

For example, selecting three numbers from a bag of balls numbered 1 to 4 would have the following 20 combinations:

111, 112, 113, 114, 122, 123, 124, 133, 134, 144, 222, 223, 224, 233, 234, 244, 333, 334, 344 and 444.

The **COMBINA **function employs the following syntax to operate:

**COMBINA(number, number_chosen)**

The **COMBINA** function has the following arguments:

**number****:**this is required and must be greater than or equal to zero. Microsoft states that**number**must be greater than or equal to**number_chosen**but this requirement does not seem to hold in practice (see my examples below)**number_chosen:**this is also required and Must be greater than or equal to zero too- non-integer values for both arguments will be truncated.

It should be further noted that:

- if the value of either argument is outside of its constraints,
**COMBINA**returns the*#NUM!*error value - if either argument is a non-numeric value,
**COMBINA**returns the*#VALUE!*error value - the following equation is used:

- in the equation above,
**N**is**number**and**M**is**number_chosen** - this function is not supported for use in DirectQuery mode when used in calculated columns or row-level security (RLS) rules.

Please see my example below:

Here, selecting four numbers from a bag of balls numbered 1 to 3 would have the following 15 combinations:

1111, 1112, 1113, 1122, 1123, 1133, 1222, 1223, 1233, 1333, 2222, 2223, 2233, 2333 and 3333.

*Come back next week for our next post on Power Pivot in the **Blog** section. In the meantime, please remember we have training in Power Pivot which you can find out more about **here**. If you wish to catch up on past articles in the meantime, you can find all of our Past Power Pivot blogs **here**.*