Within the Waves application in TekDrive, you can use Real-Time Expressions to transform your data. This allows you to make changes and calculations on your data without having to export your data to another application.
Syntax
Expressions are prefixed with the "=" character.
Signal Identifiers
Input signals are enclosed in [ ].
example: =[temp_f]*2
Number Literal
Numbers can be specified as integers (0 1234), hexadecimal integers (0xF 0x123F), binary integers (0b1 0b1011), decimals (0.21 123.456), and scientific notation (0e6 10e+5 0.1e-8).
String Literal
Strings are enclosed " ".
example: =[message1] == "hello"
Escape Sequence
Special characters can be escaped using \ .
example: =[signal\[0\]]*2
Unicode escape sequences: \u00 \x0000 \{#00000}
Multiple Inputs, Operators, and Methods in one Expression
Any number of input data streams, operators, and functions can be combined into a single expression. Data streams, operators, and functions can be repeated as many times as desired in a single expression.
example (computes dew point °F from temperature °F and relative humidity by converting to Celsius then back to Fahrenheit):
=convert(convert([Temperature (F)],"F","C")-((100-[Relative Humidity])/5),"C","F")
Long Expressions - Multi-Line Editing
Whitespace characters (newlines, tabs, spaces) are ignored in all expressions. Newlines will automatically increase the height of the edit field.
Constant Assignment
You can assign an expression to a constant (e.g. =1, ="hello"). This is particularly useful when you want to set a default value for an expression to display in a tile in case the evaluated expression returns an empty set (e.g. =([temp_f] < -60) | "No Values Under -60 Found!" ).
Operators
| Operator | Description | Example |
|---|---|---|
| + | Add two numbers | =[temp_f]+2 |
| - | Subtract two numbers | =[temp_f]-3 |
| * | Multiply two numbers | =[temp_f]*4 |
| / | Divide two numbers | =[temp_f]/5 |
| - | Negative of a number | =-[temp_f] |
| ^ | Exponential | =[temp_f]^2 |
| % | Modulo | =[temp_f]%2 |
| & | Concatenate two strings (more info) | =[message1] & [message2] |
| | | Union of two signals (more info) | =[signal1] | [signal2] |
| == | Equality (Exact Match) Operator (more info) | =[message1] == "hello" |
| != | Inequality Operator (more info) | =[message1] != "error" |
| ~ | Partial Match Operator (more info) | =[message1] ~ "err" |
| !~ | No Partial Match Operator (more info) | =[message1] !~ "err" |
| < | Less Than Operator (more info) | =[temp_f] < 90 |
| <= | Less Than or Equal Operator (more info) | =[temp_f] <= 70 |
| > | Greater Than Operator (more info) | =[temp_f] > 0 |
| >= | Greater Than Or Equal Operator (more info) | =[temp_f] >= 1 |
| () | Group | =([temp_f]+2)/3 |
| . | Member Operator | =math.max([temp_f], 32) |
| : | Map Operator (more info) | =([temp_f]>80):"hot" |
| $ | Use Selected Signal in Waves (more info) | =$+2 |
Global Methods
| Method | Description | Example |
|---|---|---|
| convert | Numerical Unit Conversion (more info) | =convert([temp_f], "f", "c") |
| smooth | Line Graph Curve Smoothing (more info) | =smooth([temp_f]) |
| math.round | Numerical Rounding (more info) | =math.round([temp_f], 2) |
| math.sum | Cumulative sum (more info) | =math.sum([data_stream]) |
| math.mean | Cumulative average (more info) | =math.mean([data_stream]) |
| math.variance | Cumulative variance (more info) | =math.variance([data_stream]) |
| math.stdDev | Cumulative standard deviation (more info) | =math.stdDev([data_stream]) |
| math.min | Take the lesser of two numbers | =math.min([temp_f], 100) |
| math.max | Take the greater of two numbers | =math.max([temp_f], 32) |
| math.sqrt | Square root of a number | =math.sqrt([data_stream]) |
| math.sin | Sine of a number | =math.sin([data_stream]) |
| math.cos | Cosine of a number | =math.cos([data_stream]) |
| math.tan | Tangent of a number | =math.tan([data_stream]) |
| math.PI | π (constant) | =math.PI |
| math.delta | Change in value (more info) | =math.delta([data_stream]) |
| math.timeDelta | Change in time (more info) | =math.timeDelta([data_stream], "sec") |
| math.timeDerivative | Time derivative (more info) | =math.timeDerivative([data_stream], "sec") |
| i2c.addr | i2c address decode | =i2c.addr([i2c_scl],[i2c_sda]) |
| i2c.data | i2c data decode | =i2c.data([i2c_scl],[i2c_sda]) |
| i2c.rw | i2c read/write decode | =i2c.rw([i2c_scl],[i2c_sda]) |
Rounding Decimals
Round the number of decimal places in a data stream to something more readable.\
Syntax: =math.round([data stream], numberDecimalPlaces)
Example: =math.round([voltage], 1)
Unit Conversion
Apply a unit conversion to each value in a selected data stream. You can find the complete list of supported units here.
Syntax: =convert([data stream], "fromUnit", "toUnit")
Example: =convert([temp_f], "f", "c")
Filter Out Unwanted Data
Filter out unwanted data by removing specific data points and/or ranges of data values. The filter operation utilizes the real-time expression comparison operators (!==, ==, <, <=, >, >=). Comparison operations can be chained together to apply multiple filters.
Single Filter
Syntax: =[data stream] <operator> <value>
Example: =[pitch] < 3
Multiple Filters
Syntax: =[data stream] <operator1> <value1> <operator2> <value2> <operator3><value3>
Example: =[pitch] < 3 != 2.64
Search Inside a Data Stream
Search for and mark specific values or ranges inside a data stream in Waves.
Single Condition
Sytax: =[data stream] <operator> <value>
Example: =[voltage] > 10
Multiple Conditions
Syntax: =[data stream] <operator1> <value1> <operator2> <value2> <operator3><value3>
Smooth Out a Noisy Signal
Apply a smoothing filter on a numerical data stream viewed as a line graph.
Default Smoothing (assumed of a smooth factor of 0.7)
Syntax: =smooth([data stream])
Example: =smooth([gyro_x])
Specific Smooth Factor
Syntax: =smooth([data stream], smoothFactor)
Example: =smooth([gyro_x], 0.9)
Mathematically Combine Multiple Data Streams
Real-time expressions allow any number of signal combinations to be inputted into a given mathematical transformation.
Syntax: =[signal1]+[signal2]
Example: =[temperature]-((100-[humidity])/5)
Merge Multiple Data Streams Into One
Merge the data points of multiple data streams into a single data stream. This operation is like interleaving the individual data points from each data stream together. This operation uses the timestamp of each data point to create a single, merged data stream. If there are two or more data points with the same timestamp, the leftmost specified data stream will take precedence.
Merge Two Signals Into One
Syntax: =[signal1] | [signal2]
Example: =[status] | [Switch]
Merge Multiple Signals Into One
Syntax: =[signal1] | [signal2] | [signal3] | ...
Cumulative Sum
math.sum performs a cumulative sum of numerical values in a data stream.
Syntax: =math.sum([data stream])
Mean
math.mean performs a cumulative average of numerical values in a data stream.
Syntax: =math.mean([data stream])
Delta
math.delta calculates the change in value between adjacent numerical values in a data stream.
Syntax: =math.delta([data stream])
Time Delta
math.timeDelta calculates the change in time between adjacent data points in a data stream. The "unit" can be "ns", "us", "ms", "sec", "min", "hr", "day".
Syntax:=math.timeDelta([data stream], "unit")
Derivative
math.timeDerivative calculates the change in value between adjacent data points divided by the change in time between adjacent data points in a data stream. The "unit" can be "ns", "us", "ms", "sec", "min", "hr", "day".
Syntax: =math.timeDerivative([data stream], "unit")
Variance
math.variance calculates the cumulative variance of numerical values in a data stream.
This is equivalent to =math.mean([data stream]^2) - math.mean([data stream])^2.
Syntax: =math.variance([data stream])
Standard Deviation
math.stdDev calculates the cumulative (population) standard deviation of numerical values in a data stream. This is equivalent to =math.sqrt(math.variance([data stream]).
Syntax: =math.stdDev([data stream])