# Functions

Some functions have default arguments, e.g. ```year(v=vector(time()) instant-vector)```. This means that there is one argument `v` which is an instant vector, which if not provided it will default to the value of the expression `vector(time())`.

## `abs()`

`abs(v instant-vector)` returns the input vector with all sample values converted to their absolute value.

## `absent()`

`absent(v instant-vector)` returns an empty vector if the vector passed to it has any elements and a 1-element vector with the value 1 if the vector passed to it has no elements.

This is useful for alerting on when no time series exist for a given metric name and label combination.

``````absent(nonexistent{job="myjob"})
# => {job="myjob"}

absent(nonexistent{job="myjob",instance=~".*"})
# => {job="myjob"}

absent(sum(nonexistent{job="myjob"}))
# => {}
``````

In the first two examples, `absent()` tries to be smart about deriving labels of the 1-element output vector from the input vector.

## `absent_over_time()`

`absent_over_time(v range-vector)` returns an empty vector if the range vector passed to it has any elements and a 1-element vector with the value 1 if the range vector passed to it has no elements.

This is useful for alerting on when no time series exist for a given metric name and label combination for a certain amount of time.

``````absent_over_time(nonexistent{job="myjob"}[1h])
# => {job="myjob"}

absent_over_time(nonexistent{job="myjob",instance=~".*"}[1h])
# => {job="myjob"}

absent_over_time(sum(nonexistent{job="myjob"})[1h:])
# => {}
``````

In the first two examples, `absent_over_time()` tries to be smart about deriving labels of the 1-element output vector from the input vector.

## `ceil()`

`ceil(v instant-vector)` rounds the sample values of all elements in `v` up to the nearest integer.

## `changes()`

For each input time series, `changes(v range-vector)` returns the number of times its value has changed within the provided time range as an instant vector.

## `clamp()`

`clamp(v instant-vector, min scalar, max scalar)` clamps the sample values of all elements in `v` to have a lower limit of `min` and an upper limit of `max`.

Special cases: - Return an empty vector if `min > max` - Return `NaN` if `min` or `max` is `NaN`

## `clamp_max()`

`clamp_max(v instant-vector, max scalar)` clamps the sample values of all elements in `v` to have an upper limit of `max`.

## `clamp_min()`

`clamp_min(v instant-vector, min scalar)` clamps the sample values of all elements in `v` to have a lower limit of `min`.

## `day_of_month()`

`day_of_month(v=vector(time()) instant-vector)` returns the day of the month for each of the given times in UTC. Returned values are from 1 to 31.

## `day_of_week()`

`day_of_week(v=vector(time()) instant-vector)` returns the day of the week for each of the given times in UTC. Returned values are from 0 to 6, where 0 means Sunday etc.

## `days_in_month()`

`days_in_month(v=vector(time()) instant-vector)` returns number of days in the month for each of the given times in UTC. Returned values are from 28 to 31.

## `delta()`

`delta(v range-vector)` calculates the difference between the first and last value of each time series element in a range vector `v`, returning an instant vector with the given deltas and equivalent labels. The delta is extrapolated to cover the full time range as specified in the range vector selector, so that it is possible to get a non-integer result even if the sample values are all integers.

The following example expression returns the difference in CPU temperature between now and 2 hours ago:

``````delta(cpu_temp_celsius{host="zeus"}[2h])
``````

`delta` should only be used with gauges.

## `deriv()`

`deriv(v range-vector)` calculates the per-second derivative of the time series in a range vector `v`, using simple linear regression.

`deriv` should only be used with gauges.

## `exp()`

`exp(v instant-vector)` calculates the exponential function for all elements in `v`. Special cases are:

• `Exp(+Inf) = +Inf`
• `Exp(NaN) = NaN`

## `floor()`

`floor(v instant-vector)` rounds the sample values of all elements in `v` down to the nearest integer.

## `histogram_quantile()`

`histogram_quantile(φ scalar, b instant-vector)` calculates the φ-quantile (0 ≤ φ ≤ 1) from the buckets `b` of a histogram. (See histograms and summaries for a detailed explanation of φ-quantiles and the usage of the histogram metric type in general.) The samples in `b` are the counts of observations in each bucket. Each sample must have a label `le` where the label value denotes the inclusive upper bound of the bucket. (Samples without such a label are silently ignored.) The histogram metric type automatically provides time series with the `_bucket` suffix and the appropriate labels.

Use the `rate()` function to specify the time window for the quantile calculation.

Example: A histogram metric is called `http_request_duration_seconds`. To calculate the 90th percentile of request durations over the last 10m, use the following expression:

``````histogram_quantile(0.9, rate(http_request_duration_seconds_bucket[10m]))
``````

The quantile is calculated for each label combination in `http_request_duration_seconds`. To aggregate, use the `sum()` aggregator around the `rate()` function. Since the `le` label is required by `histogram_quantile()`, it has to be included in the `by` clause. The following expression aggregates the 90th percentile by `job`:

``````histogram_quantile(0.9, sum by (job, le) (rate(http_request_duration_seconds_bucket[10m])))
``````

To aggregate everything, specify only the `le` label:

``````histogram_quantile(0.9, sum by (le) (rate(http_request_duration_seconds_bucket[10m])))
``````

The `histogram_quantile()` function interpolates quantile values by assuming a linear distribution within a bucket. The highest bucket must have an upper bound of `+Inf`. (Otherwise, `NaN` is returned.) If a quantile is located in the highest bucket, the upper bound of the second highest bucket is returned. A lower limit of the lowest bucket is assumed to be 0 if the upper bound of that bucket is greater than 0. In that case, the usual linear interpolation is applied within that bucket. Otherwise, the upper bound of the lowest bucket is returned for quantiles located in the lowest bucket.

If `b` has 0 observations, `NaN` is returned. If `b` contains fewer than two buckets, `NaN` is returned. For φ < 0, `-Inf` is returned. For φ > 1, `+Inf` is returned.

## `holt_winters()`

`holt_winters(v range-vector, sf scalar, tf scalar)` produces a smoothed value for time series based on the range in `v`. The lower the smoothing factor `sf`, the more importance is given to old data. The higher the trend factor `tf`, the more trends in the data is considered. Both `sf` and `tf` must be between 0 and 1.

`holt_winters` should only be used with gauges.

## `hour()`

`hour(v=vector(time()) instant-vector)` returns the hour of the day for each of the given times in UTC. Returned values are from 0 to 23.

## `idelta()`

`idelta(v range-vector)` calculates the difference between the last two samples in the range vector `v`, returning an instant vector with the given deltas and equivalent labels.

`idelta` should only be used with gauges.

## `increase()`

`increase(v range-vector)` calculates the increase in the time series in the range vector. Breaks in monotonicity (such as counter resets due to target restarts) are automatically adjusted for. The increase is extrapolated to cover the full time range as specified in the range vector selector, so that it is possible to get a non-integer result even if a counter increases only by integer increments.

The following example expression returns the number of HTTP requests as measured over the last 5 minutes, per time series in the range vector:

``````increase(http_requests_total{job="api-server"}[5m])
``````

`increase` should only be used with counters. It is syntactic sugar for `rate(v)` multiplied by the number of seconds under the specified time range window, and should be used primarily for human readability. Use `rate` in recording rules so that increases are tracked consistently on a per-second basis.

## `irate()`

`irate(v range-vector)` calculates the per-second instant rate of increase of the time series in the range vector. This is based on the last two data points. Breaks in monotonicity (such as counter resets due to target restarts) are automatically adjusted for.

The following example expression returns the per-second rate of HTTP requests looking up to 5 minutes back for the two most recent data points, per time series in the range vector:

``````irate(http_requests_total{job="api-server"}[5m])
``````

`irate` should only be used when graphing volatile, fast-moving counters. Use `rate` for alerts and slow-moving counters, as brief changes in the rate can reset the `FOR` clause and graphs consisting entirely of rare spikes are hard to read.

Note that when combining `irate()` with an aggregation operator (e.g. `sum()`) or a function aggregating over time (any function ending in `_over_time`), always take a `irate()` first, then aggregate. Otherwise `irate()` cannot detect counter resets when your target restarts.

## `label_join()`

For each timeseries in `v`, `label_join(v instant-vector, dst_label string, separator string, src_label_1 string, src_label_2 string, ...)` joins all the values of all the `src_labels` using `separator` and returns the timeseries with the label `dst_label` containing the joined value. There can be any number of `src_labels` in this function.

This example will return a vector with each time series having a `foo` label with the value `a,b,c` added to it:

``````label_join(up{job="api-server",src1="a",src2="b",src3="c"}, "foo", ",", "src1", "src2", "src3")
``````

## `label_replace()`

For each timeseries in `v`, `label_replace(v instant-vector, dst_label string, replacement string, src_label string, regex string)` matches the regular expression `regex` against the value of the label `src_label`. If it matches, the value of the label `dst_label` in the returned timeseries will be the expansion of `replacement`, together with the original labels in the input. Capturing groups in the regular expression can be referenced with `\$1`, `\$2`, etc. If the regular expression doesn't match then the timeseries is returned unchanged.

This example will return timeseries with the values `a:c` at label `service` and `a` at label `foo`:

``````label_replace(up{job="api-server",service="a:c"}, "foo", "\$1", "service", "(.*):.*")
``````

## `ln()`

`ln(v instant-vector)` calculates the natural logarithm for all elements in `v`. Special cases are:

• `ln(+Inf) = +Inf`
• `ln(0) = -Inf`
• `ln(x < 0) = NaN`
• `ln(NaN) = NaN`

## `log2()`

`log2(v instant-vector)` calculates the binary logarithm for all elements in `v`. The special cases are equivalent to those in `ln`.

## `log10()`

`log10(v instant-vector)` calculates the decimal logarithm for all elements in `v`. The special cases are equivalent to those in `ln`.

## `minute()`

`minute(v=vector(time()) instant-vector)` returns the minute of the hour for each of the given times in UTC. Returned values are from 0 to 59.

## `month()`

`month(v=vector(time()) instant-vector)` returns the month of the year for each of the given times in UTC. Returned values are from 1 to 12, where 1 means January etc.

## `predict_linear()`

`predict_linear(v range-vector, t scalar)` predicts the value of time series `t` seconds from now, based on the range vector `v`, using simple linear regression.

`predict_linear` should only be used with gauges.

## `rate()`

`rate(v range-vector)` calculates the per-second average rate of increase of the time series in the range vector. Breaks in monotonicity (such as counter resets due to target restarts) are automatically adjusted for. Also, the calculation extrapolates to the ends of the time range, allowing for missed scrapes or imperfect alignment of scrape cycles with the range's time period.

The following example expression returns the per-second rate of HTTP requests as measured over the last 5 minutes, per time series in the range vector:

``````rate(http_requests_total{job="api-server"}[5m])
``````

`rate` should only be used with counters. It is best suited for alerting, and for graphing of slow-moving counters.

Note that when combining `rate()` with an aggregation operator (e.g. `sum()`) or a function aggregating over time (any function ending in `_over_time`), always take a `rate()` first, then aggregate. Otherwise `rate()` cannot detect counter resets when your target restarts.

## `resets()`

For each input time series, `resets(v range-vector)` returns the number of counter resets within the provided time range as an instant vector. Any decrease in the value between two consecutive samples is interpreted as a counter reset.

`resets` should only be used with counters.

## `round()`

`round(v instant-vector, to_nearest=1 scalar)` rounds the sample values of all elements in `v` to the nearest integer. Ties are resolved by rounding up. The optional `to_nearest` argument allows specifying the nearest multiple to which the sample values should be rounded. This multiple may also be a fraction.

## `scalar()`

Given a single-element input vector, `scalar(v instant-vector)` returns the sample value of that single element as a scalar. If the input vector does not have exactly one element, `scalar` will return `NaN`.

## `sgn()`

`sgn(v instant-vector)` returns a vector with all sample values converted to their sign, defined as this: 1 if v is positive, -1 if v is negative and 0 if v is equal to zero.

## `sort()`

`sort(v instant-vector)` returns vector elements sorted by their sample values, in ascending order.

## `sort_desc()`

Same as `sort`, but sorts in descending order.

## `sqrt()`

`sqrt(v instant-vector)` calculates the square root of all elements in `v`.

## `time()`

`time()` returns the number of seconds since January 1, 1970 UTC. Note that this does not actually return the current time, but the time at which the expression is to be evaluated.

## `timestamp()`

`timestamp(v instant-vector)` returns the timestamp of each of the samples of the given vector as the number of seconds since January 1, 1970 UTC.

This function was added in Prometheus 2.0

## `vector()`

`vector(s scalar)` returns the scalar `s` as a vector with no labels.

## `year()`

`year(v=vector(time()) instant-vector)` returns the year for each of the given times in UTC.

## `<aggregation>_over_time()`

The following functions allow aggregating each series of a given range vector over time and return an instant vector with per-series aggregation results:

• `avg_over_time(range-vector)`: the average value of all points in the specified interval.
• `min_over_time(range-vector)`: the minimum value of all points in the specified interval.
• `max_over_time(range-vector)`: the maximum value of all points in the specified interval.
• `sum_over_time(range-vector)`: the sum of all values in the specified interval.
• `count_over_time(range-vector)`: the count of all values in the specified interval.
• `quantile_over_time(scalar, range-vector)`: the φ-quantile (0 ≤ φ ≤ 1) of the values in the specified interval.
• `stddev_over_time(range-vector)`: the population standard deviation of the values in the specified interval.
• `stdvar_over_time(range-vector)`: the population standard variance of the values in the specified interval.
• `last_over_time(range-vector)`: the most recent point value in specified interval.
• `present_over_time(range-vector)`: the value 1 for any series in the specified interval.

Note that all values in the specified interval have the same weight in the aggregation even if the values are not equally spaced throughout the interval.