Lambda expressions
TICKscript uses lambda expressions to define transformations on data points as
well as define Boolean conditions that act as filters. Lambda expressions wrap
mathematical operations, Boolean operations, internal function calls or a
combination of all three. 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, but with its own syntax:
- All field or tag identifiers must be double quoted.
- The comparison operator for equality is
==
not=
.
All lambda expressions in TICKscript begin with the lambda:
keyword.
.where(lambda: "host" == 'server001.example.com')
In some nodes the results of a lambda expression can be captured into a new
field as a named result using the property setter .as()
.
In this way they can be used in other nodes further down the pipeline.
The internal functions of lambda expressions can be either stateless or stateful. Stateful means that each time the function is evaluated the internal state can change and will persist until the next evaluation.
For example the built-in function sigma
calculates a running mean and standard
deviation and returns the number of standard deviations the current data point
is away from the mean.
Example 1 – the sigma function
sigma("value") > 3.0
Each time that the expression is evaluated it updates the running statistics and
then returns the deviation. The simple expression in Example 1 evaluates to
false
while the stream of data points it has received remains within 3.0
standard deviations of the running mean. As soon as a value is processed that
is more than 3.0
standard deviations from the mean it evaluates to true
.
Such an expression can be used inside of a TICKscript to define powerful
alerts, as illustrated in Example 2 below.
Example 2 – TICKscript with lambda expression
stream
|from()
...
|alert()
// use an expression to define when an alert should go critical.
.crit(lambda: sigma("value") > 3.0)
Note on inadvertent type casting
Beware that numerical values declared in the TICKscript follow the parsing rules
for literals introduced in the
Syntax document. They may not be
of a suitable type for the function or operation in which they will be used.
Numerical values that include a decimal will be interpreted as floats.
Numerical values without a decimal will be interpreted as integers. When
integers and floats are used within the same expression the integer values need
to use the float()
type conversion function if a float result is desired.
Failure to observe this rule can yield unexpected results. For example, when
using a lambda expression to calculate a ratio between 0 and 1 of type float to
use in generating a percentage; and when the fields are of type integer, it might
be assumed that a subset field can be divided by the total field to get the
ratio( e.g. subset/total * 100
). Such an integer by integer division will
result in an integer value of 0. Furthermore multiplication of the result of
such an operation by the literal 100
(an integer) will also result in 0.
Casting the integer values to float will result in a valid ratio in the range
between 0 and 1, and then multiplication by the literal 100.0
(a float) will
result in a valid percentage value. Correctly written, such an operation should
look like this:
eval(lambda: float("total_error_responses")/float("total_responses") * 100.0)
.
If in the logs an error appears of the type E! mismatched type to binary operator...
, check to ensure that the fields on both sides of the operator are
of the same and the desired type.
In short, to ensure that the type of a field value is correct, use the built-in type conversion functions (see below).
Built-in functions
Stateful functions
Count
Count takes no arguments but returns the number of times the expression has been evaluated.
count() int64
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
Spread
Computes the running range of all values passed into it. The range is the difference between the maximum and minimum values received.
spread(value float64) float64
Stateless functions
Type conversion functions
Bool
Converts a string into a Boolean via Golang’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 Golang’s
strconv.ParseInt or simple
int64()
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 Golang’s
strconv.ParseFloat or simple
float64()
coercion.
A Boolean is converted to a float64 where false -> 0.0 and true -> 1.0.
float(value) float64
String
Converts a bool, int64 or float64 into an string via Golang’s strconv.Format* functions. Durations are converted to a string representation of the duration.
string(value) string
Duration
Converts an int64 or a float64 into an duration assuming the unit as specified as the 2nd argument Strings are converted to duration of the form as duration literals in TICKscript.
duration(value int64|float64, unit duration) duration
duration(value string) duration
Existence
IsPresent
Returns a Boolean value based on whether the specified field or tag key is present. Useful for filtering out data this is missing the specified field or tag.
|where(lambda: isPresent("myfield"))
This returns TRUE
if myfield
is a valid identifier and FALSE
otherwise.
Time functions
The time
field
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 |
---|---|
unixNano(t time) int64 | the number of nanoseconds elapsed since January 1, 1970 UTC (Unix time) |
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 AND hour("time") < 19
The above expression evaluates to true
if the hour of the day for the data
point falls between 0900 hours and 1900 hours.
Now
Returns the current time.
now() time
Example usage:
lambda: "expiration" < unixNano(now())
Math functions
The following mathematical functions are available. Each function is implemented via the equivalent Go function (linked in the table below for reference only).
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(pp + qq), 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 (linked in the table below for reference only).
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. |
Example:
.where(lambda: !strContains("fstype", 'nfs') OR !strContains("fstype", 'cifs'))
Human string functions
HumanBytes
Converts an int64 or a 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, 'high', 'normal'))
.as('value')
The value of the field value
in the above example will be the string high
or normal
,
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)
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