Plugins for the summary statistics framework.
Calculate the average.
Calculate the number of unique values (using the HyperLogLog algorithm).
Keep the last X observations.
Find the maximum value.
Find the minimum value.
Keep a random sample of values.
Calculate the standard deviation.
Calculate the variance.
Calculate the sum.
Keep the top-k (i.e., most frequently occurring) observations.
This plugin uses a probabilistic algorithm to count the top-k elements. The algorithm (called Space-Saving) is described in the paper Efficient Computation of Frequent and Top-k Elements in Data Streams”, by Metwally et al. (2005).
Calculate the number of unique values.