Excel 365
Information
The Excel ISOMITTED function checks whether an argument was left out of a LAMBDA call — the key to giving your custom functions optional parameters with sensible defaults.
Quick answer: default a missing LAMBDA argument:
=LAMBDA(x,[y], IF(ISOMITTED(y), x, x+y)) // y is optional
Syntax
=ISOMITTED(argument)
| Argument | Description | |
|---|---|---|
argument | Required | A LAMBDA parameter to test for omission. |
How to use it
ISOMITTED only works inside LAMBDA. Mark a parameter optional by bracketing it, then test it: if omitted, supply a default. This is what turns a rigid LAMBDA into a friendly, reusable function.
=LAMBDA(rate,[periods], rate*IF(ISOMITTED(periods),12,periods))(0.05) // periods defaults to 12
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Live demo
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Result:
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Frequently asked questions
Where can ISOMITTED be used?
Only inside a LAMBDA, to test that LAMBDA’s own parameters. It errors elsewhere.
How do I mark a parameter optional?
Bracket it in the LAMBDA signature: =LAMBDA(a,[b], ...). Then test with ISOMITTED(b).
Which versions have it?
Excel 365 (the LAMBDA-era functions).
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