Computed Fields
Define derived fields using an expression language that supports arithmetic, group aggregations, windowed temporal functions, and rate-of-change calculations. Computed fields are evaluated every tick and appear alongside raw telemetry fields in all panes.
YAML Definition
computed_fields:
- name: temp_delta
expr: "zone_temp - setpoint_temp"
unit: "°C"
- name: avg_group_temp
expr: "AVG(zone_temp, building_a)"
- name: temp_rate
expr: "RATE(zone_temp, 60)"
unit: "°C/min"
- name: efficiency_rank
expr: "RANK(efficiency, fleet, asc)"
- name: rolling_std
expr: "STDDEV_WINDOW(pressure, 300)"
unit: "kPa"Expression Language
Arithmetic
Standard operators with conventional precedence: + - * /. Division by near-zero (< 1e-12) evaluates to 0.0.
zone_temp - setpoint_temp
(actual_power / rated_power) * 100
altitude_ft * 0.3048Literals and Field References
| Type | Syntax | Example |
|---|---|---|
| Literal | Numeric constant | 42.5, 0.3048 |
| Field | Field name from data_schema | zone_temp, altitude_ft |
Group Aggregations
Aggregate a field across all entities in a named group. Takes 2 arguments: (field, group_name).
| Function | Description | Example |
|---|---|---|
| MIN(field, group) | Minimum value | MIN(zone_temp, floor_3) |
| MAX(field, group) | Maximum value | MAX(pressure, all_zones) |
| AVG(field, group) | Mean value | AVG(zone_temp, building_a) |
| SUM(field, group) | Sum of values | SUM(power_kw, plant) |
| COUNT(field, group) | Count of entities | COUNT(id, active_fleet) |
Ranking
Rank the current entity within its group. Takes 3 arguments: (field, group, asc|desc).
RANK(efficiency, fleet, asc) // 1 = lowest efficiency
RANK(speed, convoy, desc) // 1 = fastestWindowed Temporal Functions
Operate on a sliding time window of historical samples. Takes 2 arguments: (field, window_seconds). Requires FieldHistoryStore to be active (automatic when computed fields reference these functions).
| Function | Description |
|---|---|
| AVG_WINDOW(field, secs) | Mean over time window |
| MIN_WINDOW(field, secs) | Minimum over window |
| MAX_WINDOW(field, secs) | Maximum over window |
| SUM_WINDOW(field, secs) | Sum over window |
| STDDEV_WINDOW(field, secs) | Sample standard deviation |
| RATE(field, secs) | Rate of change: (latest − oldest) / dt |
| SLOPE(field, secs) | Linear regression slope over window |
Field History
The FieldHistoryStore maintains a ring buffer of timestamped samples per (entity, field) pair. Configuration:
- Max samples: 2,048 per buffer (oldest evicted on overflow)
- Max age: Automatically set to 1.2x the largest window referenced by any expression
- Push rate: One sample per simulation tick per tracked field
Evaluation Context
Each computed field is evaluated per entity per tick. The evaluator receives the current entity's snapshot, all snapshots (for group aggs), group membership maps, and the field history store. Results are injected back into the snapshot before rendering and table display.
Questions?
Reach out for help with integration, deployment, or custom domain codecs.