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</pre><pre class="rust"><code><span class="doccomment">//! Module for performing cross-validation of models.
</span><span class="kw">use </span>std::cmp;
<span class="kw">use </span>std::iter::Chain;
<span class="kw">use </span>std::slice::Iter;
<span class="kw">use </span>linalg::{BaseMatrix, Matrix};
<span class="kw">use </span>learning::{LearningResult, SupModel};
<span class="kw">use </span>learning::toolkit::rand_utils::in_place_fisher_yates;
<span class="doccomment">/// Randomly splits the inputs into k &#39;folds&#39;. For each fold a model
/// is trained using all inputs except for that fold, and tested on the
/// data in the fold. Returns the scores for each fold.
///
/// # Arguments
/// * `model` - Used to train and predict for each fold.
/// * `inputs` - All input samples.
/// * `targets` - All targets.
/// * `k` - Number of folds to use.
/// * `score` - Used to compare the outputs for each fold to the targets. Higher scores are better. See the `analysis::score` module for examples.
///
/// # Examples
/// ```
/// use rusty_machine::analysis::cross_validation::k_fold_validate;
/// use rusty_machine::analysis::score::row_accuracy;
/// use rusty_machine::learning::naive_bayes::{NaiveBayes, Bernoulli};
/// use rusty_machine::linalg::{BaseMatrix, Matrix};
///
/// let inputs = Matrix::new(3, 2, vec![1.0, 1.1,
/// 5.2, 4.3,
/// 6.2, 7.3]);
///
/// let targets = Matrix::new(3, 3, vec![1.0, 0.0, 0.0,
/// 0.0, 0.0, 1.0,
/// 0.0, 0.0, 1.0]);
///
/// let mut model = NaiveBayes::&lt;Bernoulli&gt;::new();
///
/// let accuracy_per_fold: Vec&lt;f64&gt; = k_fold_validate(
/// &amp;mut model,
/// &amp;inputs,
/// &amp;targets,
/// 3,
/// // Score each fold by the fraction of test samples where
/// // the model&#39;s prediction equals the target.
/// row_accuracy
/// ).unwrap();
/// ```
</span><span class="kw">pub fn </span>k_fold_validate&lt;M, S&gt;(model: <span class="kw-2">&amp;mut </span>M,
inputs: <span class="kw-2">&amp;</span>Matrix&lt;f64&gt;,
targets: <span class="kw-2">&amp;</span>Matrix&lt;f64&gt;,
k: usize,
score: S) -&gt; LearningResult&lt;Vec&lt;f64&gt;&gt;
<span class="kw">where </span>S: Fn(<span class="kw-2">&amp;</span>Matrix&lt;f64&gt;, <span class="kw-2">&amp;</span>Matrix&lt;f64&gt;) -&gt; f64,
M: SupModel&lt;Matrix&lt;f64&gt;, Matrix&lt;f64&gt;&gt;,
{
<span class="macro">assert_eq!</span>(inputs.rows(), targets.rows());
<span class="kw">let </span>num_samples = inputs.rows();
<span class="kw">let </span>shuffled_indices = create_shuffled_indices(num_samples);
<span class="kw">let </span>folds = Folds::new(<span class="kw-2">&amp;</span>shuffled_indices, k);
<span class="kw">let </span><span class="kw-2">mut </span>costs: Vec&lt;f64&gt; = Vec::new();
<span class="kw">for </span>p <span class="kw">in </span>folds {
<span class="comment">// TODO: don&#39;t allocate fresh buffers for every fold
</span><span class="kw">let </span>train_inputs = inputs.select_rows(p.train_indices_iter.clone());
<span class="kw">let </span>train_targets = targets.select_rows(p.train_indices_iter.clone());
<span class="kw">let </span>test_inputs = inputs.select_rows(p.test_indices_iter.clone());
<span class="kw">let </span>test_targets = targets.select_rows(p.test_indices_iter.clone());
model.train(<span class="kw-2">&amp;</span>train_inputs, <span class="kw-2">&amp;</span>train_targets)<span class="question-mark">?</span>;
<span class="kw">let </span>outputs = model.predict(<span class="kw-2">&amp;</span>test_inputs)<span class="question-mark">?</span>;
costs.push(score(<span class="kw-2">&amp;</span>outputs, <span class="kw-2">&amp;</span>test_targets));
}
<span class="prelude-val">Ok</span>(costs)
}
<span class="doccomment">/// A permutation of 0..n.
</span><span class="kw">struct </span>ShuffledIndices(Vec&lt;usize&gt;);
<span class="doccomment">/// Permute the indices of the inputs samples.
</span><span class="kw">fn </span>create_shuffled_indices(num_samples: usize) -&gt; ShuffledIndices {
<span class="kw">let </span><span class="kw-2">mut </span>indices: Vec&lt;usize&gt; = (<span class="number">0</span>..num_samples).collect();
in_place_fisher_yates(<span class="kw-2">&amp;mut </span>indices);
ShuffledIndices(indices)
}
<span class="doccomment">/// A partition of indices of all available samples into
/// a training set and a test set.
</span><span class="kw">struct </span>Partition&lt;<span class="lifetime">&#39;a</span>&gt; {
train_indices_iter: TrainingIndices&lt;<span class="lifetime">&#39;a</span>&gt;,
test_indices_iter: TestIndices&lt;<span class="lifetime">&#39;a</span>&gt;
}
<span class="attribute">#[derive(Clone)]
</span><span class="kw">struct </span>TestIndices&lt;<span class="lifetime">&#39;a</span>&gt;(Iter&lt;<span class="lifetime">&#39;a</span>, usize&gt;);
<span class="attribute">#[derive(Clone)]
</span><span class="kw">struct </span>TrainingIndices&lt;<span class="lifetime">&#39;a</span>&gt; {
chain: Chain&lt;Iter&lt;<span class="lifetime">&#39;a</span>, usize&gt;, Iter&lt;<span class="lifetime">&#39;a</span>, usize&gt;&gt;,
size: usize
}
<span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>&gt; TestIndices&lt;<span class="lifetime">&#39;a</span>&gt; {
<span class="kw">fn </span>new(indices: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>[usize]) -&gt; TestIndices&lt;<span class="lifetime">&#39;a</span>&gt; {
TestIndices(indices.iter())
}
}
<span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>&gt; Iterator <span class="kw">for </span>TestIndices&lt;<span class="lifetime">&#39;a</span>&gt; {
<span class="kw">type </span>Item = <span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>usize;
<span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>usize&gt; {
<span class="self">self</span>.<span class="number">0</span>.next()
}
}
<span class="kw">impl </span>&lt;<span class="lifetime">&#39;a</span>&gt; ExactSizeIterator <span class="kw">for </span>TestIndices&lt;<span class="lifetime">&#39;a</span>&gt; {
<span class="kw">fn </span>len(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; usize {
<span class="self">self</span>.<span class="number">0</span>.len()
}
}
<span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>&gt; TrainingIndices&lt;<span class="lifetime">&#39;a</span>&gt; {
<span class="kw">fn </span>new(left: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>[usize], right: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>[usize]) -&gt; TrainingIndices&lt;<span class="lifetime">&#39;a</span>&gt; {
<span class="kw">let </span>chain = left.iter().chain(right.iter());
TrainingIndices {
chain: chain,
size: left.len() + right.len()
}
}
}
<span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>&gt; Iterator <span class="kw">for </span>TrainingIndices&lt;<span class="lifetime">&#39;a</span>&gt; {
<span class="kw">type </span>Item = <span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>usize;
<span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>usize&gt; {
<span class="self">self</span>.chain.next()
}
}
<span class="kw">impl </span>&lt;<span class="lifetime">&#39;a</span>&gt; ExactSizeIterator <span class="kw">for </span>TrainingIndices&lt;<span class="lifetime">&#39;a</span>&gt; {
<span class="kw">fn </span>len(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; usize {
<span class="self">self</span>.size
}
}
<span class="doccomment">/// An iterator over the sets of indices required for k-fold cross validation.
</span><span class="kw">struct </span>Folds&lt;<span class="lifetime">&#39;a</span>&gt; {
num_folds: usize,
indices: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span>[usize],
count: usize
}
<span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>&gt; Folds&lt;<span class="lifetime">&#39;a</span>&gt; {
<span class="doccomment">/// Let n = indices.len(), and k = num_folds.
/// The first n % k folds have size n / k + 1 and the
/// rest have size n / k. (In particular, if n % k == 0 then all
/// folds are the same size.)
</span><span class="kw">fn </span>new(indices: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>ShuffledIndices, num_folds: usize) -&gt; Folds&lt;<span class="lifetime">&#39;a</span>&gt; {
<span class="kw">let </span>num_samples = indices.<span class="number">0</span>.len();
<span class="macro">assert!</span>(num_folds &gt; <span class="number">1 </span>&amp;&amp; num_samples &gt;= num_folds,
<span class="string">&quot;Require num_folds &gt; 1 &amp;&amp; num_samples &gt;= num_folds&quot;</span>);
Folds {
num_folds: num_folds,
indices: <span class="kw-2">&amp;</span>indices.<span class="number">0</span>,
count: <span class="number">0
</span>}
}
}
<span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>&gt; Iterator <span class="kw">for </span>Folds&lt;<span class="lifetime">&#39;a</span>&gt; {
<span class="kw">type </span>Item = Partition&lt;<span class="lifetime">&#39;a</span>&gt;;
<span class="kw">fn </span>next(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="self">Self</span>::Item&gt; {
<span class="kw">if </span><span class="self">self</span>.count &gt;= <span class="self">self</span>.num_folds {
<span class="kw">return </span><span class="prelude-val">None</span>;
}
<span class="kw">let </span>num_samples = <span class="self">self</span>.indices.len();
<span class="kw">let </span>q = num_samples / <span class="self">self</span>.num_folds;
<span class="kw">let </span>r = num_samples % <span class="self">self</span>.num_folds;
<span class="kw">let </span>fold_start = <span class="self">self</span>.count * q + cmp::min(<span class="self">self</span>.count, r);
<span class="kw">let </span>fold_size = <span class="kw">if </span><span class="self">self</span>.count &gt;= r {q} <span class="kw">else </span>{q + <span class="number">1</span>};
<span class="kw">let </span>fold_end = fold_start + fold_size;
<span class="self">self</span>.count += <span class="number">1</span>;
<span class="kw">let </span>prefix = <span class="kw-2">&amp;</span><span class="self">self</span>.indices[..fold_start];
<span class="kw">let </span>suffix = <span class="kw-2">&amp;</span><span class="self">self</span>.indices[fold_end..];
<span class="kw">let </span>infix = <span class="kw-2">&amp;</span><span class="self">self</span>.indices[fold_start..fold_end];
<span class="prelude-val">Some</span>(Partition {
train_indices_iter: TrainingIndices::new(prefix, suffix),
test_indices_iter: TestIndices::new(infix)
})
}
}
<span class="attribute">#[cfg(test)]
</span><span class="kw">mod </span>tests {
<span class="kw">use super</span>::{ShuffledIndices, Folds};
<span class="comment">// k % n == 0
</span><span class="attribute">#[test]
</span><span class="kw">fn </span>test_folds_n6_k3() {
<span class="kw">let </span>idxs = ShuffledIndices(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>]);
<span class="kw">let </span>folds = collect_folds(Folds::new(<span class="kw-2">&amp;</span>idxs, <span class="number">3</span>));
<span class="macro">assert_eq!</span>(folds, <span class="macro">vec!</span>[
(<span class="macro">vec!</span>[<span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>], <span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>]),
(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">4</span>, <span class="number">5</span>], <span class="macro">vec!</span>[<span class="number">2</span>, <span class="number">3</span>]),
(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>], <span class="macro">vec!</span>[<span class="number">4</span>, <span class="number">5</span>])
]);
}
<span class="comment">// k % n == 1
</span><span class="attribute">#[test]
</span><span class="kw">fn </span>test_folds_n5_k2() {
<span class="kw">let </span>idxs = ShuffledIndices(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>]);
<span class="kw">let </span>folds = collect_folds(Folds::new(<span class="kw-2">&amp;</span>idxs, <span class="number">2</span>));
<span class="macro">assert_eq!</span>(folds, <span class="macro">vec!</span>[
(<span class="macro">vec!</span>[<span class="number">3</span>, <span class="number">4</span>], <span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>]),
(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>], <span class="macro">vec!</span>[<span class="number">3</span>, <span class="number">4</span>])
]);
}
<span class="comment">// k % n == 2
</span><span class="attribute">#[test]
</span><span class="kw">fn </span>test_folds_n6_k4() {
<span class="kw">let </span>idxs = ShuffledIndices(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>]);
<span class="kw">let </span>folds = collect_folds(Folds::new(<span class="kw-2">&amp;</span>idxs, <span class="number">4</span>));
<span class="macro">assert_eq!</span>(folds, <span class="macro">vec!</span>[
(<span class="macro">vec!</span>[<span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>], <span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>]),
(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">4</span>, <span class="number">5</span>], <span class="macro">vec!</span>[<span class="number">2</span>, <span class="number">3</span>]),
(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">5</span>], <span class="macro">vec!</span>[<span class="number">4</span>]),
(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>], <span class="macro">vec!</span>[<span class="number">5</span>])
]);
}
<span class="comment">// k == n
</span><span class="attribute">#[test]
</span><span class="kw">fn </span>test_folds_n4_k4() {
<span class="kw">let </span>idxs = ShuffledIndices(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>]);
<span class="kw">let </span>folds = collect_folds(Folds::new(<span class="kw-2">&amp;</span>idxs, <span class="number">4</span>));
<span class="macro">assert_eq!</span>(folds, <span class="macro">vec!</span>[
(<span class="macro">vec!</span>[<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>], <span class="macro">vec!</span>[<span class="number">0</span>]),
(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">2</span>, <span class="number">3</span>], <span class="macro">vec!</span>[<span class="number">1</span>]),
(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">3</span>], <span class="macro">vec!</span>[<span class="number">2</span>]),
(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>], <span class="macro">vec!</span>[<span class="number">3</span>])
]);
}
<span class="attribute">#[test]
#[should_panic]
</span><span class="kw">fn </span>test_folds_rejects_large_k() {
<span class="kw">let </span>idxs = ShuffledIndices(<span class="macro">vec!</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>]);
<span class="kw">let _ </span>= collect_folds(Folds::new(<span class="kw-2">&amp;</span>idxs, <span class="number">4</span>));
}
<span class="comment">// Check we&#39;re really returning iterators into the shuffled
// indices rather than into (0..n).
</span><span class="attribute">#[test]
</span><span class="kw">fn </span>test_folds_unordered_indices() {
<span class="kw">let </span>idxs = ShuffledIndices(<span class="macro">vec!</span>[<span class="number">5</span>, <span class="number">4</span>, <span class="number">3</span>, <span class="number">2</span>, <span class="number">1</span>, <span class="number">0</span>]);
<span class="kw">let </span>folds = collect_folds(Folds::new(<span class="kw-2">&amp;</span>idxs, <span class="number">3</span>));
<span class="macro">assert_eq!</span>(folds, <span class="macro">vec!</span>[
(<span class="macro">vec!</span>[<span class="number">3</span>, <span class="number">2</span>, <span class="number">1</span>, <span class="number">0</span>], <span class="macro">vec!</span>[<span class="number">5</span>, <span class="number">4</span>]),
(<span class="macro">vec!</span>[<span class="number">5</span>, <span class="number">4</span>, <span class="number">1</span>, <span class="number">0</span>], <span class="macro">vec!</span>[<span class="number">3</span>, <span class="number">2</span>]),
(<span class="macro">vec!</span>[<span class="number">5</span>, <span class="number">4</span>, <span class="number">3</span>, <span class="number">2</span>], <span class="macro">vec!</span>[<span class="number">1</span>, <span class="number">0</span>])
]);
}
<span class="kw">fn </span>collect_folds&lt;<span class="lifetime">&#39;a</span>&gt;(folds: Folds&lt;<span class="lifetime">&#39;a</span>&gt;) -&gt; Vec&lt;(Vec&lt;usize&gt;, Vec&lt;usize&gt;)&gt; {
folds
.map(|p|
(p.train_indices_iter.map(|x| <span class="kw-2">*</span>x).collect::&lt;Vec&lt;<span class="kw">_</span>&gt;&gt;(),
p.test_indices_iter.map(|x| <span class="kw-2">*</span>x).collect::&lt;Vec&lt;<span class="kw">_</span>&gt;&gt;()))
.collect::&lt;Vec&lt;(Vec&lt;usize&gt;, Vec&lt;usize&gt;)&gt;&gt;()
}
}
</code></pre></div>
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