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NaN (Not a Number)

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The danger of NaN

In Java, NaN has the property that NaN != NaN. This is a problem when storing NaN in a numeric dictionary, as the dictionary uses == to compare values. This means that the value will never be found and each instance of NaN will be mapped to a new value in the dictionary. It leads to an ever-growing dictionary, wasting memory, and potential bad result in queries.

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How to handle NaN:

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Do not dictionarize a field containing NaN

It is ok to have some NaN values in the datastore as long as the field storing the value is not dictionarized. For instance, such field can be used as a measure.

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Try to avoid using NaN

If you need to dictionarize the field to use it as a hierarchy, then try to avoid using NaN:
  • Use another special value as the marker for “no value”, for instance null, Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY, Double.MAX_VALUE…
  • Use a String column with N/A and parse the value when you need it as double (parse N/A the same way you would use NaN)
  • Use 2 columns: one String and one double (you can have one column calculated based on the other) and use the String column as the hierarchy and the numeric column for measures.

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Type the column as Object

You can also type the column as Object instead of Double, so it uses an object dictionary which compares values with Object.equals(...). As NaN.equals(Nan) is true, the dictionary will be able to correctly match the NaN.