Steffen Müller > Math-SZaru > Math::SZaru::TopEstimator

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NAME ^

Math::SZaru::TopEstimator - Statistical estimator of the 'top N' items based on CountSketch algorithm

SYNOPSIS ^

  use Math::SZaru::TopEstimator;
  my $ue = Math::SZaru::TopEstimator->new($num_top_elems_to_track);
  $ue->add_elem("foo");
  $ue->add_weighted_elem("bar", 100); # same as ->add_elem times 100
  $ue->add_elems("foo", "bar"); # same as ->add_elem for each one
  $ue->add_weighted_elems("foo" => 10, "bar" => 20);
  # add many more elems ...
  
  my $inserted_elems_count = $ue->tot_elems;
  my $estimated_list_of_top_elements = $ue->estimate();
  
  # $estimated_list_of_top_elements is now something like:
  # [ ["most frequent string", $count], ["second most frequent string, $count],
  #   [...], [...], ..., ["nth most frequent string", $count] ]

DESCRIPTION ^

Math::SZaru::TopEstimator provides a statistical estimate of the 'top N' most frequent data items in a stream. This is based on CountSketch algorithm from "Finding Frequent Items in Data Streams", Moses Charikar, Kevin Chen and Martin Farach-Colton, 2002.

METHODS ^

new

Constructor. Expects an integer indicating the number of "top" items to track.

add_elem

Given a string, adds the string to the TopEstimator.

add_elems

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

add_weighted_elem

Given a string and a count N, adds that string N times to the estimator (with a weight of N). Functionality-wise same as calling doing $est->add_elem("foo") for 1..$N, but much faster.

add_weighted_elems

This is to add_weighted_elem what add_elems is to add_elem. Takes a list of string, count, string, count, ....

tot_elems

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

estimate

Returns a reference to an array containing as many records as were configured to be tracked at construction time. Each record, in order, represents the n-th most frequent item in the input stream -- estimated.

Each record is a reference to an array of the value (string) and its' estimated total number of occurrences in the input.

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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