Ubidots Analytics Engine supports a complex mathematical computation tool called Synthetic Variables. In simple words, a variable is any raw data within a device in Ubidots, and a synthetic variable is a variable that results from the computation of other variables within Ubidots.

This tool allows you to extend your application's functionality. For example, if you develop a temperature logger that reads the variable in °C and you wish to show the data in both °C and °F you would retrieve the sensor change and send two values to Ubidots: one value in °C and another one in °F. This adds (an unnecessary) compute load to your microcontroller, but using the Ubidots' Analytics Engine you need to only send the raw value in °C, and let Ubidots perform the required calculations to convert to ºF, alleviating the excess microcontroller processing requirements.

Synthetic computation example: From Celsius to Fahrenheit

Here, you will learn the basics about Synthetic Variables and the available mathematical and statistical functions you can implement using this tool.

IMPORTANT NOTE: The synthetic variables engine's computational speed is heavily influenced by the synthetic expression complexity, which results in calculation times ranging from a few seconds to a few minutes.

Table of Contents:

  1. Creating a synthetic variable

  2. List of supported expressions

  3. Mathematical expressions

  4. Data Range expressions

  5. Rolling expressions

  6. Advanced expressions

  7. Setting synthetic variable timezone

  8. Results

1. Creating a synthetic variable

Ubidots stores dots that come from your devices as default variables, and these data have corresponding timestamps that organize each one of them into a time-series list, using the following sequence:


With Ubidots Analytics Engine, you can apply different operations to the time-series data-set to create an adjacent data-set containing computed variables; these new variables are called Synthetic Variables. To create one, click on the "Add new variable" option within your device, then select Synthetic.

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2. List of supported expressions

Go to Ubidots developer center to learn more about the supported functions, or click here to download a PDF with the list.

3. Mathematical expressions

A synthetic variable consists of a math operation applied to the whole time series:

In the above figure, a square root expression is applied to the time series data.

Find below the list of supported mathematical expressions:

Syntax

Description

ceil(x)

Returns the rounded integer greater or equal for each element in the variable x. The ceil function always rounds up to the nearest integer.

floor(x) 

Returns the floor of x as an integer, the largest integer value less than or equal to x.

round(x, n steps)

Returns the floating point value number rounded to "n" digits after the decimal point.

sin(x) 

Returns the sine in radians of each element in the variable x.

cos(x) 

Returns the cosine in radians of each element in the variable x.

tan(x) 

Returns the tangent of each element in the variable x.

arcsin(x) 

Returns in radians the inverse sine of each element in the variable x.

arcos(x) 

Returns in radians the inverse sine of each element in the variable x.

artan2(x, y) 

Returns in radians the inverse tangent of each element in the variable x.

artan2(x) 

Returns in radians the trigonometric inverse tangent using the input variables x and y as Cartesian coordinates.

Note: It will only perform the operation between values with the same timestamp.

sinh(x) 

Returns the hyperbolic sine of each element in the variable x.

cosh(x) 

Returns the hyperbolic cosine of each element in the variable x.

tanh(x) 

Returns the hyperbolic tangent of each element in the variable x.

arcsinh(x) 

Returns in radians the inverse hyperbolic sine of each element in the variable x.

arcosh(x) 

Returns in radians the inverse hyperbolic cosine of each element in the variable x.

arctanh(x) 

Returns in radians the inverse hyperbolic tangent of each element in the variable x.

exp(x) 

Returns the exponential of each element in the variable x.

log(x, base) 

Returns the logarithm of each element in the variable x. By default, the base is the Euler's number.

abs(x) 

Returns the absolute value of each element in the variable x.

sqrt(x) 

Returns the square root value of each element in the variable x.

Standard arithmetic operations and mathematical constants work just fine too:

  • Addition: +

  • Subtraction: - 

  • Division: /

  • Multiplication: *

  • Exponentiation: **

  • Module: %

  • π : pi

  • Euler's number: e 

Example:

Convert a temperature value from °C to °F :

F = ((9 / 5) * variable) + 32

The synthetic editor will look as follows:

4. Data range expressions

Ubidots allows you to create new variables from your time series based on date range data, i.e calculate average temperature per hour or day based on your sensor's readings using a synthetic variable.

Below you can find the commonly used data range functions and formula structure:

Syntax

Description

max(x, range) 

Returns the maximum value of the variable x in the specified date range.

min(x, range) 

Returns the minimum value of the variable x in the specified date range.

mean(x, range) 

Returns the mean value of the variable x in the specified date range.

std(x, range) 

Returns the standard deviation of the variable x in the specified date range.

count(x, range) 

Returns the number of dots stored in the variable x for the specified date range.

last(x, range) 

Returns the last value of the time-series variable x in the specified date range.

first(x, range) 

Returns the first value of the time-series variable x in the specified date range.

sum(x, range) 

Returns the sum of the dots stored in the variable x in the specified date range.

Available data ranges:

  • "nT" : Every n minutes

  • "nH" : Every n hours

  • "nD" : Every n days 

  • "W" :  Every end of week 

  • "M" : Every end of month 

IMPORTANT NOTE: The selected range should be set in a way that evenly divides the next range. For example, if using minutes ("T"), whatever the number is, it has to evenly divide an hour ("H"). Under such example, the available values for minutes are: 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30. Other values may render unexpected results. The same applies to other ranges

Example:
The average temperature every 10 minutes in °F

A = mean( ((9 / 5) * variable) + 32, "10T" )

The expression should looks as follows:

Example:

Every n data range starts its period at 00:00:00, however, there are particular applications where the desired starting point is not 00:00:00 but rather 02:00:00 or 00:40:00, depending on the input data range. To apply an offset, the above functions can receive a third parameter called offset, as follows:

A = sum(variable, "8H", offset=6)

The above example corresponds to the sum of variable computed every 8 hours, offset by 6 hours (beyond 00:00:00), that is, 06:00:00. Accordingly, the synthetic variable will be run at 6:00, 14:00, and 22:00 daily.


5. Rolling expressions

This function returns the computed value of a data series within a time window or a given number of values, using one of the following aggregation methods: "mean", "sum", "min", "max", or "count".

rolling (variable, aggregation_method, type_range, range, min_periods = 2)

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Example:

Calculate the maximum value of a sample of four data points.

rolling(variable,"max","values",4)

6. Advanced Functions

There are additional functions for more complex operations:

where ( )

where(condition, operation_if_true, operation_if_false)

Computes operation_if_true if the condition is True, or operation_if_false if the condition is false.


Comparison statements:

  • Equal to: ==

  • Greater than: >

  • Lower than: <

  • Not equal to: !=

  • Equal to, greater than: >=

  • Equal to, lower than: <=

Logical expressions (useful when setting more than 1 condition):

  • And: "and"

  • Or: "or"

Examples

Populates the new synthetic variable with a '1 (true)' if the temperature value is greater than 20:

where({{var}} > 20, 1)

Populates the synthetic variable with a '1' if the temperature value is greater than 20, if not, fills with a '0' value.

where({{var}} > 20, 1, 0)

Stores the variables' timestamp if it is lower than 20 OR greater than 50:

where({{var}} < 20 or {{var}} > 50, {{var}}.timestamp)

As you can see, the dot, '.' operator lets you access and represents the variable's timestamp.

diff ( )

This function calculates the difference staring at the last element in a time series and the next separated by a specified number of steps.

diff(x, step)

shift ( )

The function returns the variable's values in the time series shifted by the given number of steps.

shift(x,step)

cumsum ( )

This function returns the cumulative sum of a time series.

cumsum(x)

fill_missing ( )

fill_missing(x)

Computes an expression containing multiple variables with different timestamps, filling any non-equal timestamped values with the non-equal variable´s last value.


Example:

fill_missing(3 * var1_id + var2_id)

  • Obtain the context value of a variable

{YOUR_VARIABLE}.context.context-key

Context data can only be used within your synthetic expression if the context is a number.

  • Obtain the timestamp of a variable

{YOUR_VARIABLE}.timestamp

Similar to retrieving context data, you can retrieve the timestamp of a variable using the dot '.' operator. For more information about advanced functions, check out this article: Analytics: Advanced Synthetic Variables

7. Setting synthetic variables timezone

The synthetic variables editor allows you to select the timezone to reference the exact variable's timestamps based on a particular timezone. This comes in handy when your clients are located in a different country and need to see the data in their timezone.

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After clicking the Accept button, the synthetic variable will calculate data based on the selected timezone and the results will be automatically saved as a time series variable.

8. Results

Now you're ready to start creating analytics and insights from your data using Ubidots' Analytics Engine and the Synthetic Variables. For additional troubleshooting and inquiries, check out the Ubidots Community not only Ubidots will help, but also your fellow users who may experience the same errors.

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