<p>In <a href="https://github.com/mlpack/mlpack/pull/749#discussion_r76077253">src/mlpack/methods/lsh/lshmodel_impl.hpp</a>:</p>
<pre style='color:#555'>> + maxKValue = k;
> +
> + // Save pointer to training set.
> + this->referenceSet = &referenceSet;
> +
> + // Step 1. Select a random sample of the dataset. We will work with only that
> + // sample.
> + arma::vec sampleHelper(referenceSet.n_cols, arma::fill::randu);
> +
> + // Keep a sample of the dataset: We have uniformly random numbers in [0, 1],
> + // so we expect about N*sampleRate of them to be in [0, sampleRate).
> + arma::mat sampleSet = referenceSet.cols(
> + arma::find(sampleHelper < sampleRate));
> + // Shuffle to be impartial (in case dataset is sorted in some way).
> + sampleSet = arma::shuffle(sampleSet);
> + const size_t numSamples = sampleSet.n_cols; // Points in sampled set.
</pre>
<p>I think it's without replacement: I generate uniform numbers in [0, 1] and then threshold at the sample rate, getting a vector of booleans. I keep only columns (so, points) that have "true" in the corresponding vector position:<br>
In matlab/pseudocode it would be:</p>
<div class="highlight highlight-source-matlab"><pre>sampleRate = <span class="pl-c1">0.3</span>;
referenceSet = [
<span class="pl-c1">1</span> <span class="pl-c1">3</span> <span class="pl-c1">5</span> <span class="pl-c1">7</span>;
<span class="pl-c1">2</span> <span class="pl-c1">4</span> <span class="pl-c1">6</span> <span class="pl-c1">8</span>;
]
sampleHelper = [<span class="pl-c1">0.1</span> <span class="pl-c1">0.3</span> <span class="pl-c1">0.7</span> <span class="pl-c1">0.05</span>];
sampleHelper = sampleHelper <span class="pl-k">></span> sampleRate;
<span class="pl-c">% So here sampleHelper = [0 0 1 0]</span>
sampleSet = referenceSet.cols(sampleHelper);
<span class="pl-c">% and therefore sampleSet = [5; 6] - only column 3</span></pre></div>
<p>Is there something I don't see here?</p>
<p>I didn't know about <code>ObtainDistinctSamples()</code>, I think that will make the code cleaner so I'll refactor it to use that instead.</p>
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