## Description

The reservoir sampling step 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 step uses uniform sampling; all incoming rows have an equal chance of being selected. This step is particularly useful when used in conjunction with the ARFF output step in order to generate a suitable sized data set to be used by WEKA. The reservoir sampling step uses Algorithm R by Jeffery Vitter.

## Options

Option |
Description |

Step name |
The name of this step as it appears in the transformation workspace. |

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 transformation with a different value for the seed will result in a different random sample being chosen. |

## References

Vitter, J. S. Random Sampling with a Reservoir. ACM Transactions on Mathematical Software, Vol. 11, No. 1, March 1985. Pages 37-57.