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= Reservoir Sampling

== Description

The Reservoir Sampling transform allows you to sample a fixed number of rows from an incoming data stream when the total number of incoming rows is not known in advance. The transform uses uniform sampling; all incoming rows have an equal chance of being selected. This transform is particularly useful when used in conjunction with the ARFF output transform in order to generate a suitable sized data set to be used by WEKA. The reservoir sampling transform uses link:https://en.wikipedia.org/wiki/Reservoir_sampling[Algorithm R] by Jeffery Vitter.

== Options

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|===
|Option|Description
|Transform name|Name of the transform this name has to be unique in a single pipeline.
|Sample size|Select how many rows to sample from an incoming stream. Setting a value of 0 will cause all rows to be sampled; setting a negative value will block all rows.
|Random seed|Choose a seed for the random number generator. Repeating a pipeline with a different value for the seed will result in a different random sample being chosen. 
|===