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Derived Metrics

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Derived metrics can be used to compute new values by using an expression based on the value of other metrics. The expression can be used to compute a numeric, a boolean or a string value.

Creating a Derived metric

To add a new Derived metric to a Thing Definition, you should:

  1. Enter the Computed Data page.
  2. Select the Thing Definitions tab.
  3. Select the Thing Definition to edit.
  4. Press the Add Metric button.
  5. Select the Derived type and provide the required information.
  6. Press the Save button and edit the additional information, if needed.

Editing a Derived metric

In the main configuration panel, it is possible to select one or more metrics or properties to use within the expression.

Once the metrics/properties have been selected, it is possible to configure the derivation expression.

Pressing the Add Condition button, it is possible to add multiple result conditions to implement the IF, ELSE, OTHERWISE pattern. 

Null Result

In case the result expression, of the activated case (including the default one) is empty, no new data is stored in the database.
For instance:
  • IF metric1 > 100 -> left the result empty to do nothing
  • ELSE RETURN (metric1 + metric2) -> save new value

Expressions

The expression language used to define Derived Metric expressions is based on the following operators.

OPERATOR

NOTATION

SAMPLE

Mathematical

+ - * / % ^

(x + y^2)/4

Logical

or and true/false

x==y && (b==true || b==c)

Relational

= != < ⇐ > >

a != b

Elvis

Ternary operator

condition ? foo : bar
It is possible to use this predefined set of functions.

MATHEMATICAL

DESCRIPTION

SAMPLE

cos

Returns the trigonometric cosine of an angle, in radians.

#cos(x)

sen

Returns the trigonometric sine of an angle, in radians.

#sen(x)

abs

Returns the absolute value of a numeric value.

#abs(x)

sqrt

Returns the rounded positive square root of a numeric value.

#sqrt(x)

pi

The PI value (3.14159…​).

#pi

ceil

Returns the smallest integer value greater than or equal to the float argument.

#ceil(x)

floor

Returns the largest integer value that is less than or equal to the float argument.

#floor(x)

log

Returns the natural logarithm (base e) of the argument.

#log(x)

log10

Returns the base 10 logarithm of the argument.

#log(x)

max

Returns the greater of two values.

#max(x, y)

min

Returns the smallest of two values.

#min(x, y)

pow

Returns the value of the first argument raised to the power of the second argument.

#pow(x, exp)

CONVERSION

DESCRIPTION

SAMPLE

parseInt

Converts the string argument to integer using the given radix (optional).

#parseInt('12') or #parseInt('BF123', 16)

intToString

Converts an integer to string using a radix.

#intToString(x, 16)

parseFloat

Converts the string argument to float using the given radix (optional).

#parseFloat('12') or #parseFloat('BF123', 16)

floatToString

Converts a float to string using a radix.

#floatToString(x, 16)

toString

Converts the source value to string.

var.#toString()

STRING

DESCRIPTION

SAMPLE

substring

Returns a substring considering the start (inclusive) and end (exclusive) zero based indexes.

str.#substring(startIndex) or str.#substring(startIndex, endIndex)

length

Returns the length of the string.

str.#length()

charAt

Returns the character at the specified index.

str.#charAt(index)

indexOf

Returns the index (zero-based) of the first occurrence of the argument string.

str.#indexOf('foo')

lastIndexOf

Returns the index (zero-based) of the last occurrence of the argument string.

str.#lastIndexOf('foo')

split

Returns the arrays of tokens splitting by the argument string.

str.#split(',')

upperCase

Converts the source string to upper-case.

str.#toUpperCase()

lowerCase

Converts the source string to lower case.

str.#toLowerCase()

 

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