Steffen Müller > Math-SZaru > Math::SZaru::UniqueEstimator

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Math-SZaru-0.01.tar.gz

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NAME ^

Math::SZaru::UniqueEstimator - Statistical estimator for total number of unique items

SYNOPSIS ^

  use Math::SZaru::UniqueEstimator;
  my $ue = Math::SZaru::UniqueEstimator->new($maxelems);
  $ue->add_elem("foo");
  # add many more elems using add_elem ...
  my $inserted_elems_count = $ue->tot_elems;
  my $estimated_unique_count = $ue->estimate();

DESCRIPTION ^

Math::SZaru::UniqueEstimator provides a statistical estimate of the number of unique elements in the input stream.

Quoting the documentation of the SZaru C++ implementation:

  The technique used is:
  - Convert all elements to unique evenly spaced hash keys.
  - Keep track of the smallest N element ("nElemes") of these elements.
  - "nelems" cannot glow beyond maxelems.
  - Based on the coverage of the space, compute an estimate
  of the total number of unique elements, where biggest-small-elem
  means largest element among kept "maxelems" elements.
  
  unique = nElemes < maxelems
  ? nElems
  : (maxelems << bits-in-hash) / biggest-small-elem

METHODS ^

new

Constructor. Expects an integer indicating the total size of the underlying hash table.

add_elem

Given a string, adds the string to the UniqueEstimator hash table.

add_elems

Same as add_elem, but accepts an arbitrary number of strings to insert into the estimator at once.

tot_elems

Returns the total count of the number of elements that were added to the estimator.

estimate

Returns the estimated number of unique elements that were added to the estimator so far. See above for a description of the algorithm.

SEE ALSO ^

Math::SZaru

SZaru: "SZaru/" in llamerada.github.com

Sawzall: http://code.google.com/p/szl/

AUTHOR ^

Steffen Mueller, <smueller@cpan.org>

COPYRIGHT AND LICENSE ^

The Perl wrapper of the SZaru library is:

Copyright (C) 2013 by Steffen Mueller

Just like SZaru itself, it is licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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