OPAL Alignment Functions

Alignment functions are used with the align verb to align metrics to time windows.

Alignment functions accept an input metric time series and emit a value for each row. For example, last_not_null will return the final non-null measurement for each time window of a series.

Function	Description
any	Return any value of one column across a group
any_not_null	Return any non-null value of one column across a group.
avg	Calculate the arithmetic average of the input expression across the group, or of the scalar arguments if more than one.
count	Count the number of non-null items in the group.
count_distinct	Estimate the approximate number of distinct values in the input using hyper-log-log.
count_distinct_exact	Count the exact number of distinct values in the input using complete enumeration.
delta	Calculates the value difference of the argument in each time bin for each group.
delta_monotonic	Calculates the amount of difference in a column in each time bin for each group.
deriv	Calculate the average per-second derivative of the argument across the group.
first	Return the first value of one column across an ordered group.
first_not_null	Return the first non-null value of one column across an ordered group.
last	Return the last value of one column across an ordered group.
last_not_null	Return the last non-null value of one column across an ordered group.
max	Returns the maximum value of a group of inputs.
median	Return the fast approximate median value of one column.
median_exact	Return the exact median value of one column.
min	Returns the minimum value of a group of inputs.
percentile	Returns an approximated value for the specified percentile of the input expression across the group.
percentile_cont	Assuming a continuous distribution, return the value for the specified percentile of the input expression across the group.
percentile_disc	Assuming a discrete distribution, return the value for the specified percentile of the input expression across the group.
rate	Calculate the average per-second rate of the argument across the group.
stddev	Calculate the standard deviation across the group.
sum	Calculate the sum of the argument across the group, or of the scalar arguments if more than one.
tdigest_agg	Generate a single t-digest state out of an arbitrary number of numeric values.
tdigest_combine	Combine (merge) multiple t-digest values together This function is purely an aggregate function.
topk_agg	Returns an approximation of the top K most frequent values in the input, along with their approximate frequencies.