iff | Axiom Docs

iff

This page explains how to use the iff function in APL.

Introduction

The iff function evaluates a single Boolean predicate and returns one of two values depending on the result. Use it to add binary flag columns, choose between two computed expressions, or conditionally override a value in one step.

The iif function is an alias for iff and behaves identically. For three or more branches, use case instead.

Usage

Syntax

iff(predicate, ifTrue, ifFalse)

Parameters

Name	Type	Required	Description
predicate	bool	Yes	Expression that evaluates to `true` or `false`.
ifTrue	scalar	Yes	Value returned when `predicate` is `true`.
ifFalse	scalar	Yes	Value returned when `predicate` is `false`. Must be the same type as `ifTrue`.

Returns

The value of ifTrue when predicate evaluates to true, or ifFalse otherwise.

Use case examples

Flag requests that take longer than one second to identify slow endpoints.

Query

['sample-http-logs']
| extend is_slow = iff(req_duration_ms > 1000, 'slow', 'fast')
| summarize count() by is_slow

Run in Playground

Output

is_slow	count_
fast	9630
slow	501

The query adds a is_slow column to each request and then counts how many fall into each category.

Label spans as long or short based on their duration to get a quick overview of latency distribution per service.

Query

['otel-demo-traces']
| extend is_long = iff(duration > 500ms, 'long', 'short')
| summarize count() by is_long, ['service.name']

Run in Playground

Output

is_long	service.name	count_
short	frontend	4210
short	cart	1830
long	checkout	423
long	product-catalog	182

The query shows how many spans per service exceed the 500 ms threshold.

case: Multi-branch conditional that evaluates a list of conditions and returns the first matching result. Use case when you have three or more outcomes.
coalesce: Returns the first non-null value from a list of expressions. Use coalesce when you want to fall back from null rather than branch on a condition.