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i stumbled across the following challenge in FME:

how to deal with NULL values if you want to perform a calculation for a new attribute. For example, I want to sum up values (could be any other kind of arithmetics).

The expected result is fine as long as no NULL Value is involved. FME turns any calculation into a NULL result if any NULL is involved (see documentation).

Result using a numeric expression ---------------------- Result using a non-numeric expression to illustrate
enter image description here enter image description here

The question that haunts me is, how to treat those NULL values as 0 in the calculation without changing the value to an actual 0 (as the NullAttributeMapper would).

The result I am looking for is the following:

If all values are NULL i want the result to be NULL, otherwise I want the NULL value to be treated as 0. Furthermore, I dont want the NULL values to be changed to 0, so I can distinguish between NULL and 0 in further calculations.

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The AttributeManager has a functionality to handle NULL as 0 (or any other value you like), without tampering with the orignal values.

res0

The result is what i was looking for:

Result using a numeric expression in combination with a condition to preserve NULL
res2
Result using a non-numeric expression to illustrate
res1
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  • Yes, that's the best way. Another way would be to use a NullAttributeMapper transformer first, assuming you're OK with replacing the values permanently.
    – Mark Ireland
    Dec 21, 2022 at 16:17

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