| %%% |
| %%% Copyright 2011, Boundary |
| %%% |
| %%% 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. |
| %%% |
| |
| |
| %%%------------------------------------------------------------------- |
| %%% File: folsom_sample_uniform.erl |
| %%% @author joe williams <j@boundary.com> |
| %%% @doc |
| %%% erlang implementation of a uniform random sample |
| %%% based on a java implementation by coda hale, which can be found at: |
| %%% |
| %%% https://github.com/codahale/metrics/blob/development/src/main/java/com/yammer/metrics/core/UniformSample.java |
| %%% |
| %%% that implementation is based on algorithm R in: |
| %%% |
| %%% http://www.cs.umd.edu/~samir/498/vitter.pdf |
| %%% @end |
| %%%----------------------------------------------------------------- |
| |
| -module(folsom_sample_uniform). |
| |
| -export([ |
| new/1, |
| update/2, |
| get_values/1 |
| ]). |
| |
| -include("folsom.hrl"). |
| |
| new(Size) -> |
| #uniform{size = Size}. |
| |
| update(#uniform{size = Size, reservoir = Reservoir, n = N} = Sample, Value) when N =< Size -> |
| ets:insert(Reservoir, {N, Value}), |
| Sample#uniform{n = N + 1}; |
| |
| update(#uniform{reservoir = Reservoir, size = Size, n = N, seed = Seed} = Sample, |
| Value) -> |
| {Rnd, New_seed} = random:uniform_s(N, Seed), |
| maybe_update(Rnd, Size, Value, Reservoir), |
| Sample#uniform{n = N + 1, seed = New_seed}. |
| |
| get_values(#uniform{reservoir = Reservoir}) -> |
| {_, Values} = lists:unzip(ets:tab2list(Reservoir)), |
| Values. |
| |
| maybe_update(Rnd, Size, Value, Reservoir) when Rnd < Size -> |
| ets:insert(Reservoir, {Rnd, Value}); |
| maybe_update(_Rnd, _Size, _Value, _Reservoir) -> |
| ok. |