Lambda Expressions | InfluxData Documentation Archive

TICKscript uses lambda expressions to define transformations on data points as well as define boolean conditions that act as filters. TICKscript tries to be similar to InfluxQL in that most expressions that you would use in an InfluxQL WHERE clause will work as expressions in TICKscript. There are few exceptions:

All field or tag identifiers must be double quoted.
The comparison operator for equality is == not =.

All expressions in TICKscript begin with the lambda: keyword.

.where(lambda: "host" == 'server001.example.com')

Stateful

These lambda expressions are stateful, meaning that each time they are evaluated internal state can change and will persist until the next evaluation. This may seem odd as part of an expression language but it has a powerful use case. You can define a function within the language that is essentially a online/streaming algorithm and with each call the function state is updated. For example the built-in function sigma that calculates a running mean and standard deviation and returns the number of standard deviations the current data point is away from the mean.

Example:

sigma("value") > 3

Each time that the expression is evaluated the new value it updates the running statistics and then returns the deviation. This simple expression evaluates to false while the stream of data points it has received remains within 3 standard deviations of the running mean. As soon as a value is processed that is more than 3 standard deviation it evaluates to true. Now you can use that expression inside of a TICKscript to define powerful alerts.

TICKscript with lambda expression:

stream
    .alert()
        // use an expression to define when an alert should go critical.
.crit(lambda: sigma("value") > 3)

Builtin Functions

Bool

Converts a string into a boolean via Go’s strconv.ParseBool

bool(value string) bool

Int

Converts a string or float64 into an int64 via Go’s strconv.ParseInt or simple float64() coercion. Strings are assumed to be decimal numbers.

int(value float64 or string) int64

Float

Converts a string or int64 into an float64 via Go’s strconv.ParseFloat or simple int64() coercion.

float(value int64 or string) float64

Sigma

Computes the number of standard deviations a given value is away from the running mean. Each time the expression is evaluated the running mean and standard deviation are updated.

sigma(value float64) float64

Count

Count takes no arguments but returns the number of times the expression has been evaluated.

count() int64

Math functions

The following mathematical functions are available. Each function is implemented via the equivalent Go function. Short descriptions are provided here but see the Go docs for more details.

Function	Description
abs	Abs returns the absolute value of x.

acos	Acos returns the arccosine, in radians, of x.

acosh	Acosh returns the inverse hyperbolic cosine of x.

asin	Asin returns the arcsine, in radians, of x.

asinh	Asinh returns the inverse hyperbolic sine of x.

atan	Atan returns the arctangent, in radians, of x.

atan2	Atan2 returns the arc tangent of y/x, using the signs of the two to determine the quadrant of the return value.

atanh	Atanh returns the inverse hyperbolic tangent of x.

cbrt	Cbrt returns the cube root of x.

ceil	Ceil returns the least integer value greater than or equal to x.

cos	Cos returns the cosine of the radian argument x.

cosh	Cosh returns the hyperbolic cosine of x.

erf	Erf returns the error function of x.

erfc	Erfc returns the complementary error function of x.

exp	Exp returns e**x, the base-e exponential of x.

exp2	Exp2 returns 2**x, the base-2 exponential of x.

expm1	Expm1 returns e**x - 1, the base-e exponential of x minus 1.