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.


Technically speaking, the um function requires an extra five characters to do the same work as the traditional + sign.

So, why does MetrixND include this function?

In the situation where variable has 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.


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 means 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 does not matter whether you use traditional math operators or the functions when data are 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 purposes.

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Mark Quan
Principal Forecast Consultant - Itron