The Sum function in **MetrixND** seems like a complex way to make adding difficult.

In a MetrixND transformation, numbers are added by joining variables with the “+” sign. Adding three variables is as simple as writing the following expression in the transformation editor formula box:

*DataSource.Variable1 + DataSource.Variable2 + DataSource.Variable3*

The complex way to add is using the “Sum” function. This function requires inserting the three variables separated by commas (,) as Sum function parameters, as shown below:

*Sum(DataSource.Variable1,DataSource.Variable2,DataSource.Variable3)*

Technically speaking, the Sum function requires five extra characters to do the same work as the traditional “+” sign.

So, why does MetrixND include this function?

In the situation where variables have missing values, the calculation using the “+” sign results in a missing value. In other words, a number plus a missing value equals a missing value.

*100 + MISSING = MISSING*

While the Sum function behaves the same, the Ignore Missing option changes the behavior to produce a value. In other words, the Sum function with the Ignore Missing option selected means that a number plus a missing value equals a number.

*100 + MISSING = 100*

To activate the Ignore Missing option, check the Ignore Missing box in the transformation editor as shown below.

The Ignore Missing options works with the following functions:

- Sum
- Avg
- Max
- Min

It doesn’t matter whether you use traditional math operators or the functions when data is complete. However, when the dataset has missing values, the functions and Ignore Missing options may be the difference between forecasting a number and forecasting a MISSING.

Complexity has its purpose.