Andrew Shvayka
1 year ago
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<!-- [TODO]: [Calculated Fields] add content --> |
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#### Calculated field TBEL script function |
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The **calculate()** function is a user-defined script that allows you to perform custom calculations using [TBEL{:target="_blank"}](${siteBaseUrl}/docs${docPlatformPrefix}/user-guide/tbel/) on telemetry and attribute data. |
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It receives arguments configured in the calculated field setup and an additional `ctx` object, which provides access to all arguments. |
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##### Function signature |
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```javascript |
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function calculate(ctx, arg1, arg2, ...): object | object[] |
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``` |
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##### Argument representation in the script |
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Before describing how arguments are passed to the function, let's define how different argument types are **represented** inside the script. |
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There are two types of arguments that can be used in the function: |
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* single value arguments - represent the latest telemetry data or attribute. |
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```json |
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{ |
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"altitude": { |
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"ts": 1740644636669, |
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"value": 1034 |
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} |
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} |
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``` |
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* when accessed via `ctx.args`, they remain objects: |
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```javascript |
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var altitudeTimestamp = ctx.args.altitude.ts; |
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var altitudeValue = ctx.args.altitude.value; |
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``` |
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* when accessed as a **function parameter**, only the value is passed: |
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```javascript |
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function calculate(ctx, altitude/*(single value argument)*/, temperature/*(time series rolling argument)*/) { |
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// altitude = 1035 |
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} |
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``` |
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* time series rolling arguments - contain historical data within a defined time window. |
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```json |
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{ |
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"temperature": { |
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"timeWindow": { |
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"startTs": 1740643762896, |
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"endTs": 1740644662896 |
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}, |
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"values": [ |
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{ "ts": 1740644355935, "value": 72.32 }, |
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{ "ts": 1740644365935, "value": 72.86 }, |
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{ "ts": 1740644375935, "value": 73.58 }, |
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{ "ts": 1740644385935, "value": "NaN" } |
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] |
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} |
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} |
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``` |
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* when accessed via `ctx.args`, they remain rolling argument objects: |
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```javascript |
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var startOfInterval = temperature.timeWindow.startTs; |
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var firstTimestamp = temperature.values[0].ts; |
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var firstValue = temperature.values[0].value; |
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``` |
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* when accessed as a **function parameter**, they are passed as rolling arguments, retaining their structure: |
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```javascript |
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function calculate(ctx, altitude/*(single value argument)*/, temperature/*(time series rolling argument)*/) { |
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var avgTemp = temperature.mean(); // Use rolling argument functions |
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} |
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``` |
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**Built-in methods for rolling arguments** |
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Time series rolling arguments provide built-in functions for calculations. |
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These functions accept an optional `ignoreNaN` boolean parameter, which controls how NaN values are handled. |
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Each function has two function signatures: |
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* **Without parameters:** `method()` → called **without parameters** and defaults to `ignoreNaN = true`, meaning NaN values are ignored. |
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* **With an explicit parameter:** `method(boolean ignoreNaN)` → called with a boolean `ignoreNaN` parameter: |
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* `true` → ignores NaN values (default behavior). |
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* `false` → includes NaN values in calculations. |
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| Method | Default Behavior (`ignoreNaN = true`) | Alternative (`ignoreNaN = false`) | |
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|------------|--------------------------------------------------|---------------------------------------------| |
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| `max()` | Returns the highest value, ignoring NaN values. | Returns NaN if any NaN values exist. | |
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| `min()` | Returns the lowest value, ignoring NaN values. | Returns NaN if any NaN values exist. | |
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| `mean()` | Computes the average value, ignoring NaN values. | Returns NaN if any NaN values exist. | |
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| `std()` | Calculates the standard deviation, ignoring NaN. | Returns NaN if any NaN values exist. | |
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| `median()` | Returns the median value, ignoring NaN values. | Returns NaN if any NaN values exist. | |
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| `count()` | Counts only valid (non-NaN) values. | Counts all values, including NaN. | |
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| `last()` | Returns the most recent non-NaN value. | Returns the last value, even if it is NaN. | |
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| `first()` | Returns the oldest non-NaN value. | Returns the first value, even if it is NaN. | |
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| `sum()` | Computes the total sum, ignoring NaN values. | Returns NaN if any NaN values exist. | |
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The following calculations are executed over the provided above arguments: |
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**Usage: default (`ignoreNaN = true`)** |
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```javascript |
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var avgTemp = temperature.mean(); |
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var tempMax = temperature.max(); |
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var valueCount = temperature.count(); |
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``` |
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**Output:** |
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```json |
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{ |
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"avgTemp": 72.92, |
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"tempMax": 73.58, |
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"valueCount": 3 |
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} |
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``` |
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**Usage: explicit (`ignoreNaN = false`)** |
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```javascript |
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var avgTemp = temperature.mean(false); // Returns NaN if any NaN values exist |
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var tempMax = temperature.max(false); // Returns NaN if any NaN values exist |
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var valueCount = temperature.count(false); // Counts all values, including NaN |
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``` |
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**Output:** |
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```json |
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{ |
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"avgTemp": "NaN", |
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"tempMax": "NaN", |
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"valueCount": 4 |
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} |
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``` |
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Time series rolling arguments can be **merged** to align timestamps across multiple datasets. |
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| Method | Description | Parameters | Returns | |
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|:-----------------------------|:-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|:-------------------------------------------------| |
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| `merge(other, settings)` | Merges the current rolling argument with another rolling argument by aligning timestamps and filling missing values with the previous available value. | <ul><li>`other` (another rolling argument)</li><li>`settings` (optional) - configuration object, supports:<ul><br/><li>`ignoreNaN` (boolean, default true) - controls whether NaN values should be ignored.</li><li>`timeWindow` (object, default {}) - defines a custom time window for filtering merged values.</li></ul></li></ul>| Merged object with timeWindow and aligned values. | |
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| `mergeAll(others, settings)` | Merges the current rolling argument with multiple rolling arguments by aligning timestamps and filling missing values with the previous available value. | <ul><li>`others` (array of rolling arguments)</li><li>`settings` (optional) - configuration object, supports:<ul><br/><li>`ignoreNaN` (boolean, default true) - controls whether NaN values should be ignored.</li><li>`timeWindow` (object, default {}) - defines a custom time window for filtering merged values.</li></ul></li></ul>| Merged object with timeWindow and aligned values.| |
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**Example arguments:** |
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```json |
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{ |
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"humidity": { |
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"timeWindow": { |
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"startTs": 1741356332086, |
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"endTs": 1741357232086 |
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}, |
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"values": [{ |
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"ts": 1741356882759, |
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"value": 43 |
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}, { |
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"ts": 1741356918779, |
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"value": 46 |
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}] |
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}, |
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"pressure": { |
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"timeWindow": { |
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"startTs": 1741356332086, |
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"endTs": 1741357232086 |
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}, |
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"values": [{ |
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"ts": 1741357047945, |
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"value": 1023 |
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}, { |
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"ts": 1741357056144, |
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"value": 1026 |
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}, { |
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"ts": 1741357147391, |
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"value": 1025 |
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}] |
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}, |
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"temperature": { |
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"timeWindow": { |
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"startTs": 1741356332086, |
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"endTs": 1741357232086 |
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}, |
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"values": [{ |
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"ts": 1741356874943, |
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"value": 76 |
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}, { |
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"ts": 1741357063689, |
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"value": 77 |
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}] |
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} |
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} |
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``` |
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**Usage:** |
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```javascript |
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var mergedData = temperature.merge(humidity, { ignoreNaN: false }); |
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``` |
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**Output:** |
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```json |
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{ |
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"mergedData": { |
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"timeWindow": { |
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"startTs": 1741356332086, |
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"endTs": 1741357232086 |
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}, |
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"values": [{ |
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"ts": 1741356874943, |
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"values": [76.0, "NaN"] |
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}, { |
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"ts": 1741356882759, |
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"values": [76.0, 43.0] |
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}, { |
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"ts": 1741356918779, |
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"values": [76.0, 46.0] |
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}, { |
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"ts": 1741357063689, |
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"values": [77.0, 46.0] |
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}] |
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} |
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} |
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``` |
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**Usage:** |
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```javascript |
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var mergedData = temperature.mergeAll([humidity, pressure], { ignoreNaN: true }); |
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``` |
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**Output:** |
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```json |
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{ |
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"mergedData": { |
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"timeWindow": { |
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"startTs": 1741356332086, |
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"endTs": 1741357232086 |
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}, |
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"values": [{ |
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"ts": 1741357047945, |
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"values": [76.0, 46.0, 1023.0] |
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}, { |
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"ts": 1741357056144, |
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"values": [76.0, 46.0, 1026.0] |
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}, { |
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"ts": 1741357063689, |
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"values": [77.0, 46.0, 1026.0] |
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}, { |
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"ts": 1741357147391, |
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"values": [77.0, 46.0, 1025.0] |
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}] |
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} |
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} |
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``` |
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##### Function arguments |
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* `ctx` - context object that contains all provided arguments, in the representations described above. |
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Accessing arguments via `ctx`: |
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```javascript |
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var altitude = ctx.args.altitude; // single value argument |
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var temperature = ctx.args.temperature; // time series rolling argument |
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``` |
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* `arg1, arg2, ...` - user-defined arguments configured in the calculated field setup. |
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How they are passed depends on their type: |
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* **single value arguments** are passed as raw values **(e.g., 22.5, "ON")**. |
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* **time series rolling arguments** are passed as objects (containing multiple values). |
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##### Example: Air Density Calculation |
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This function calculates air density using `altitude` (single value argument) and `temperature` (time series rolling argument). |
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```javascript |
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function calculate(ctx, altitude, temperature) { |
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var avgTemperature = temperature.mean(); // Get average temperature |
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var temperatureK = (avgTemperature - 32) * (5 / 9) + 273.15; // Convert Fahrenheit to Kelvin |
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// Estimate air pressure based on altitude |
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var pressure = 101325 * Math.pow((1 - 2.25577e-5 * altitude), 5.25588); |
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// Air density formula |
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var airDensity = pressure / (287.05 * temperatureK); |
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return { |
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"airDensity": airDensity |
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}; |
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} |
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``` |
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* `altitude` is a single value, passed as number. |
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* `temperature` is a rolling argument, retaining its full structure. |
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##### Function return format |
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The script should return a JSON object formatted according to the [ThingsBoard Telemetry Upload API](${siteBaseUrl}/docs${docPlatformPrefix}/user-guide/telemetry/#time-series-data-upload-api/). |
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The return value must match one of the supported telemetry upload formats. |
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The script must return data in a format compatible with ThingsBoard’s APIs. |
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The correct return format depends on the calculated field output configuration: |
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* if latest telemetry is used for output, the function must return data according to the [Telemetry Upload API](${siteBaseUrl}/docs${docPlatformPrefix}/reference/mqtt-api/#attributes-api/). |
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* without timestamps |
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```json |
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{ |
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"airDensity": 1.06, |
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"someKey": "value" |
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} |
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``` |
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* with a timestamp: |
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```json |
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{ |
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"ts": 1740644636669, |
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"values": { |
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"airDensity": 1.06, |
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"someKey": "value" |
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} |
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} |
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``` |
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* if attributes are used for output, the function must return data according to the [Attributes API](${siteBaseUrl}/docs${docPlatformPrefix}/user-guide/telemetry/#time-series-data-upload-api/). |
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```json |
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{ |
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"airDensity": 1.06, |
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"someKey": "value" |
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} |
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``` |
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