# The latest Event

`latest(a)` gives access to the most recent Confirmed Event of Rule `a`, whether still running or Ended:

- `.min(x)`, `.max(x)`, `.mean(x)`: its [Aggregates](https://romanhaendler.github.io/rbed/aggregates/) of Channel `x`, so far if it is running. Rule `a` aggregates `x` for this automatically.
- `.duration()`: its duration in milliseconds, up to now if it is running.

Each is an Expression, undefined while there has been no Event of `a`. This relates the present to an earlier Event.

## A partial set-down

A crane lifts a load of 800 kg from 10 s to 40 s and sets it down to 300 kg in between, from 25 s to 30 s. Then it lifts 600 kg from 60 s to 90 s and sets it down to 350 kg from 75 s to 80 s. `LoadLifted` has an End Condition, so a set-down does not End it. `PartialSetDown` holds while the weight is below a fraction of the latest lift's maximum.

Parameters (in the page address as ?fraction=…):

- Fraction of the maximum (`fraction`): 0.1 to 0.9 in steps of 0.05, default 0.5

The site cannot run the default parameters: (JavaScript) TypeError: Cannot read properties of undefined (reading 'length')

Java source at the default parameters:

```java
import static io.github.romanhaendler.rbed.Conditions.*;

import io.github.romanhaendler.rbed.*;
import java.util.Map;

Channel weight = Channel.named("weight");

Rule loadLifted = Rule.named("LoadLifted").when(weight.above(500)).endWhen(weight.below(50));
Rule partialSetDown = Rule.named("PartialSetDown")
    .when(during(loadLifted).and(weight.below(latest(loadLifted).max(weight).times(0.5))));
Detector detector = Detector.builder()
    .rules(loadLifted, partialSetDown)
    .build();

for (int s = 0; s <= 110; s++) {   // one Sample a second
  double kg = s >= 25 && s < 30 ? 300
      : s >= 10 && s < 40 ? 800
      : s >= 75 && s < 80 ? 350
      : s >= 60 && s < 90 ? 600
      : 0;
  detector.push(s * 1_000L, Map.of(weight, kg));
}
detector.close();
```

At the default fraction of 0.5:

- Before 10 s there has been no lift, and `latest(loadLifted).max(weight)` is undefined.
- During the first lift `latest` reads that lift, whose maximum is 800 kg. The set-down to 300 kg is below 400 kg, and `PartialSetDown` runs from 25 s to 30 s.
- Between the lifts `latest` still reads the first one, which has Ended, but `during(loadLifted)` does not hold.
- From 60 s `latest` reads the second lift. Its maximum is 600 kg, so its set-down to 350 kg is not below 300 kg, although it would be below half of the first lift's 800 kg.

### Things to try

- Raise the fraction to 0.6: the second set-down counts too. 350 kg is below 360 kg, and `PartialSetDown` runs from 75 s to 80 s.
- Lower it to 0.3: neither set-down is below 240 kg or 180 kg, and there is no `PartialSetDown`.

## A cycle taking too long

`.duration()` of a running Event grows with time, so a Rule can detect a long Event while it is still running:

```java
Rule cycle = Rule.named("Cycle").when(spindle.above(0.5));
Rule slowCycle = Rule.named("SlowCycle")
    .when(during(cycle).and(latest(cycle).duration().above(Duration.ofMinutes(2).toMillis())));
```

The [Cranes](https://romanhaendler.github.io/rbed/cranes/) example uses `PartialSetDown` with lifting, overload and classifying a load.

## Reference

- [latest: values of the most recent Event](https://github.com/romanhaendler/rbed#latest-values-of-the-most-recent-event) and [Aggregates](https://github.com/romanhaendler/rbed#aggregates) in the README, the canonical text
- [LatestEvent](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/LatestEvent.html) in the Javadoc

Methods used: [`Channel.named`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Channel.html#named%28java.lang.String%29), [`Rule.named`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Rule.html#named%28java.lang.String%29), [`Rule.when`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Rule.html#when%28io.github.romanhaendler.rbed.Condition%29), [`Expression.above`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Expression.html#above%28double%29), [`Rule.endWhen`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Rule.html#endWhen%28io.github.romanhaendler.rbed.Condition%29), `Expression.below` ([double](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Expression.html#below%28double%29), [Expression](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Expression.html#below%28io.github.romanhaendler.rbed.Expression%29)), [`Conditions.during`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Conditions.html#during%28io.github.romanhaendler.rbed.Rule%29), [`Condition.and`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Condition.html#and%28io.github.romanhaendler.rbed.Condition%29), [`Conditions.latest`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Conditions.html#latest%28io.github.romanhaendler.rbed.Rule%29), [`LatestEvent.max`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/LatestEvent.html#max%28io.github.romanhaendler.rbed.Channel%29), [`Expression.times`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Expression.html#times%28double%29), [`Detector.builder`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Detector.html#builder%28%29), [`Detector.Builder.rules`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Detector.Builder.html#rules%28io.github.romanhaendler.rbed.Rule...%29), [`Detector.Builder.build`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Detector.Builder.html#build%28%29), [`Detector.push`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Detector.html#push%28long,java.util.Map%29), [`Detector.close`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/Detector.html#close%28%29), [`LatestEvent.duration`](https://romanhaendler.github.io/rbed/api/io.github.romanhaendler.rbed/io/github/romanhaendler/rbed/LatestEvent.html#duration%28%29).