Lambda Expressions

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

Type Conversion functions

Bool

Converts a string into a boolean via Go’s strconv.ParseBool function. Numeric types can also be converted to a bool where a 0 -> false and 1 -> true.

bool(value) 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. Durations are converted into an int64 with nanoseconds units. A boolean is converted to an int64 where false -> 0 and true -> 1.

int(value) int64

Float

Converts a string or int64 into an float64 via Go’s strconv.ParseFloat or simple int64() coercion. A boolean is converted to an float64 where false -> 0.0 and true -> 1.0.

float(value) float64

String

Converts a bool, int64 or float64 into an string via Go’s strconv.Format* functions. Durations are converted to a string representation of the duration.

string(value) string

Duration

Converts a int64 or float64 into an duration assuming nanoseconds units. Strings are converted to duration of the form as duration literals in TICKscript.

duration(value) duration

Stateful Functions

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

Time functions

Within each expression the time field contains the time of the current data point. The following functions can be used on the time field. Each function returns an int64.

Function	Description
minute(t time) int64	the minute within the hour: range [0,59]
hour(t time) int64	the hour within the day: range [0,23]
weekday(t time) int64	the weekday within the week: range [0,6], 0 is Sunday
day(t time) int64	the day within the month: range [1,31]
month(t time) int64	the month within the year: range [1,12]
year(t time) int64	the year

Example usage:

lambda: hour("time") == 9

The above expression evaluates to true if the hour of the day for the data point is 9 AM, using local time.

Math functions

The following mathematical functions are available. Each function is implemented via the equivalent Go function.

Function	Description
abs(x float64) float64	Abs returns the absolute value of x.
acos(x float64) float64	Acos returns the arccosine, in radians, of x.
acosh(x float64) float64	Acosh returns the inverse hyperbolic cosine of x.
asin(x float64) float64	Asin returns the arcsine, in radians, of x.
asinh(x float64) float64	Asinh returns the inverse hyperbolic sine of x.
atan(x float64) float64	Atan returns the arctangent, in radians, of x.
atan2(y, x float64) float64	Atan2 returns the arc tangent of y/x, using the signs of the two to determine the quadrant of the return value.
atanh(x float64) float64	Atanh returns the inverse hyperbolic tangent of x.
cbrt(x float64) float64	Cbrt returns the cube root of x.
ceil(x float64) float64	Ceil returns the least integer value greater than or equal to x.
cos(x float64) float64	Cos returns the cosine of the radian argument x.
cosh(x float64) float64	Cosh returns the hyperbolic cosine of x.
erf(x float64) float64	Erf returns the error function of x.
erfc(x float64) float64	Erfc returns the complementary error function of x.
exp(x float64) float64	Exp returns e**x, the base-e exponential of x.
exp2(x float64) float64	Exp2 returns 2**x, the base-2 exponential of x.
expm1(x float64) float64	Expm1 returns e**x - 1, the base-e exponential of x minus 1. It is more accurate than Exp(x) - 1 when x is near zero.
floor(x float64) float64	Floor returns the greatest integer value less than or equal to x.
gamma(x float64) float64	Gamma returns the Gamma function of x.
hypot(p, q float64) float64	Hypot returns Sqrt(p*p + q*q), taking care to avoid unnecessary overflow and underflow.
j0(x float64) float64	J0 returns the order-zero Bessel function of the first kind.
j1(x float64) float64	J1 returns the order-one Bessel function of the first kind.
jn(n int64, x float64) float64	Jn returns the order-n Bessel function of the first kind.
log(x float64) float64	Log returns the natural logarithm of x.
log10(x float64) float64	Log10 returns the decimal logarithm of x.
log1p(x float64) float64	Log1p returns the natural logarithm of 1 plus its argument x. It is more accurate than Log(1 + x) when x is near zero.
log2(x float64) float64	Log2 returns the binary logarithm of x.
logb(x float64) float64	Logb returns the binary exponent of x.
max(x, y float64) float64	Max returns the larger of x or y.
min(x, y float64) float64	Min returns the smaller of x or y.
mod(x, y float64) float64	Mod returns the floating-point remainder of x/y. The magnitude of the result is less than y and its sign agrees with that of x.
pow(x, y float64) float64	Pow returns x**y, the base-x exponential of y.
pow10(x int64) float64	Pow10 returns 10**e, the base-10 exponential of e.
sin(x float64) float64	Sin returns the sine of the radian argument x.
sinh(x float64) float64	Sinh returns the hyperbolic sine of x.
sqrt(x float64) float64	Sqrt returns the square root of x.
tan(x float64) float64	Tan returns the tangent of the radian argument x.
tanh(x float64) float64	Tanh returns the hyperbolic tangent of x.
trunc(x float64) float64	Trunc returns the integer value of x.
y0(x float64) float64	Y0 returns the order-zero Bessel function of the second kind.
y1(x float64) float64	Y1 returns the order-one Bessel function of the second kind.
yn(n int64, x float64) float64	Yn returns the order-n Bessel function of the second kind.

String functions

The following string manipulation functions are available. Each function is implemented via the equivalent Go function.

Function	Description
strContains(s, substr string) bool	StrContains reports whether substr is within s.
strContainsAny(s, chars string) bool	StrContainsAny reports whether any Unicode code points in chars are within s.
strCount(,s sep string) int64	StrCount counts the number of non-overlapping instances of sep in s. If sep is an empty string, Count returns 1 + the number of Unicode code points in s.
strHasPrefix(s, prefix string) bool	StrHasPrefix tests whether the string s begins with prefix.
strHasSuffix(s, suffix string) bool	StrHasSuffix tests whether the string s ends with suffix.
strIndex(s, sep string) int64	StrIndex returns the index of the first instance of sep in s, or -1 if sep is not present in s.
strIndexAny(s, chars string) int64	StrIndexAny returns the index of the first instance of any Unicode code point from chars in s, or -1 if no Unicode code point from chars is present in s.
strLastIndex(s, sep string) int64	StrLastIndex returns the index of the last instance of sep in s, or -1 if sep is not present in s.
strLastIndexAny(s, chars string) int64	StrLastIndexAny returns the index of the last instance of any Unicode code point from chars in s, or -1 if no Unicode code point from chars is present in s.
strLength(s string) int64	StrLength returns the length of the string.
strReplace(s, old, new string, n int64) string	StrReplace returns a copy of the string s with the first n non-overlapping instances of old replaced by new.
strSubstring(s string, start, stop int64) string	StrSubstring returns a substring based on the given indexes, strSubstring(str, start, stop) is equivalent to str[start:stop] in Go.
strToLower(s string) string	StrToLower returns a copy of the string s with all Unicode letters mapped to their lower case.
strToUpper(s string) string	StrToUpper returns a copy of the string s with all Unicode letters mapped to their upper case.
strTrim(s, cutset string) string	StrTrim returns a slice of the string s with all leading and trailing Unicode code points contained in cutset removed.
strTrimLeft(s, cutset string) string	StrTrimLeft returns a slice of the string s with all leading Unicode code points contained in cutset removed.
strTrimPrefix(s, prefix string) string	StrTrimPrefix returns s without the provided leading prefix string. If s doesn’t start with prefix, s is returned unchanged.
strTrimRight(s, cutset string) string	StrTrimRight returns a slice of the string s, with all trailing Unicode code points contained in cutset removed.
strTrimSpace(s string) string	StrTrimSpace returns a slice of the string s, with all leading and trailing white space removed, as defined by Unicode.
strTrimSuffix(s, suffix string) string)	StrTrimSuffix returns s without the provided trailing suffix string. If s doesn’t end with suffix, s is returned unchanged.
regexReplace(r regex, s, pattern string) string	RegexReplace replaces matches of the regular expression in the input string with the output string. For example regexReplace(/a(b*)c/, ‘abbbc’, ‘group is $1’) -> ‘group is bbb’. The original string is returned if no matches are found.

Human String functions

HumanBytes

Converts a int64 or float64 with units bytes into a human readable string representing the number of bytes.

humanBytes(value) string

Conditional Functions

If

Returns the result of its operands depending on the value of the first argument. The second and third arguments must return the same type.

Example:

|eval(lambda: if("field" > threshold AND "field" != 0, 'true', 'false'))
    .as('value')

The value of the field value in the above example will be the string true or false, depending on the condition passed as the first argument.

The if function’s return type is the same type as its second and third arguments.

if(condition, true expression, false expression)