Support sampling integers from discrete distributions

src/distribution/bernoulli.rs

@@ -84,11 +84,19 @@
     }
 }
 
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
+impl ::rand::distributions::Distribution<bool> for Bernoulli {
+    fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> bool {
+        rng.gen_bool(self.p())
+    }
+}
+
 #[cfg(feature = "rand")]
 #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
 impl ::rand::distributions::Distribution<f64> for Bernoulli {
     fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> f64 {
-        rng.gen_bool(self.p()) as u8 as f64
+        rng.sample::<bool, _>(self) as u8 as f64
     }
 }
 

src/distribution/binomial.rs

@@ -111,19 +111,27 @@
 
 #[cfg(feature = "rand")]
 #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
-impl ::rand::distributions::Distribution<f64> for Binomial {
-    fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> f64 {
-        (0..self.n).fold(0.0, |acc, _| {
+impl ::rand::distributions::Distribution<u64> for Binomial {
+    fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> u64 {
+        (0..self.n).fold(0, |acc, _| {
             let n: f64 = rng.gen();
             if n < self.p {
-                acc + 1.0
+                acc + 1
             } else {
                 acc
             }
         })
     }
 }
 
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
+impl ::rand::distributions::Distribution<f64> for Binomial {
+    fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> f64 {
+        rng.sample::<u64, _>(self) as f64
+    }
+}
+
 impl DiscreteCDF<u64, f64> for Binomial {
     /// Calculates the cumulative distribution function for the
     /// binomial distribution at `x`

src/distribution/categorical.rs

@@ -123,11 +123,27 @@
     }
 }
 
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
+impl ::rand::distributions::Distribution<usize> for Categorical {
+    fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> usize {
+        sample_unchecked(rng, &self.cdf)
+    }
+}
+
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
+impl ::rand::distributions::Distribution<u64> for Categorical {
+    fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> u64 {
+        sample_unchecked(rng, &self.cdf) as u64
+    }
+}
+
 #[cfg(feature = "rand")]
 #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
 impl ::rand::distributions::Distribution<f64> for Categorical {
     fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> f64 {
-        sample_unchecked(rng, &self.cdf)
+        sample_unchecked(rng, &self.cdf) as f64
     }
 }
 
@@ -325,13 +341,9 @@
 /// without doing any bounds checking
 #[cfg(feature = "rand")]
 #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
-pub fn sample_unchecked<R: ::rand::Rng + ?Sized>(rng: &mut R, cdf: &[f64]) -> f64 {
+pub fn sample_unchecked<R: ::rand::Rng + ?Sized>(rng: &mut R, cdf: &[f64]) -> usize {
     let draw = rng.gen::<f64>() * cdf.last().unwrap();
-    cdf.iter()
-        .enumerate()
-        .find(|(_, val)| **val >= draw)
-        .map(|(i, _)| i)
-        .unwrap() as f64
+    cdf.iter().position(|val| *val >= draw).unwrap()
 }
 
 /// Computes the cdf from the given probability masses. Performs

src/distribution/discrete_uniform.rs

@@ -74,11 +74,19 @@
     }
 }
 
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
+impl ::rand::distributions::Distribution<i64> for DiscreteUniform {
+    fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> i64 {
+        rng.gen_range(self.min..=self.max)
+    }
+}
+
 #[cfg(feature = "rand")]
 #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
 impl ::rand::distributions::Distribution<f64> for DiscreteUniform {
     fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> f64 {
-        rng.gen_range(self.min..=self.max) as f64
+        rng.sample::<i64, _>(self) as f64
     }
 }
 

src/distribution/geometric.rs

@@ -92,19 +92,28 @@
 
 #[cfg(feature = "rand")]
 #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
-impl ::rand::distributions::Distribution<f64> for Geometric {
-    fn sample<R: ::rand::Rng + ?Sized>(&self, r: &mut R) -> f64 {
-        use ::rand::distributions::OpenClosed01;
-
+impl ::rand::distributions::Distribution<u64> for Geometric {
+    fn sample<R: ::rand::Rng + ?Sized>(&self, r: &mut R) -> u64 {
         if ulps_eq!(self.p, 1.0) {
-            1.0
+            1
         } else {
-            let x: f64 = r.sample(OpenClosed01);
-            x.log(1.0 - self.p).ceil()
+            let x: f64 = r.sample(::rand::distributions::OpenClosed01);
+            // This cast is safe, because the largest finite value this expression can take is when
+            // `x = 1.4e-45` and `1.0 - self.p = 0.9999999999999999`, in which case we get
+            // `930262250532780300`, which when casted to a `u64` is `930262250532780288`.
+            x.log(1.0 - self.p).ceil() as u64
         }
     }
 }
 
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
+impl ::rand::distributions::Distribution<f64> for Geometric {
+    fn sample<R: ::rand::Rng + ?Sized>(&self, r: &mut R) -> f64 {
+        r.sample::<u64, _>(self) as f64
+    }
+}
+
 impl DiscreteCDF<u64, f64> for Geometric {
     /// Calculates the cumulative distribution function for the geometric
     /// distribution at `x`

src/distribution/hypergeometric.rs

@@ -147,17 +147,17 @@
 
 #[cfg(feature = "rand")]
 #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
-impl ::rand::distributions::Distribution<f64> for Hypergeometric {
-    fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> f64 {
+impl ::rand::distributions::Distribution<u64> for Hypergeometric {
+    fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> u64 {
         let mut population = self.population as f64;
         let mut successes = self.successes as f64;
         let mut draws = self.draws;
-        let mut x = 0.0;
+        let mut x = 0;
         loop {
             let p = successes / population;
             let next: f64 = rng.gen();
             if next < p {
-                x += 1.0;
+                x += 1;
                 successes -= 1.0;
             }
             population -= 1.0;
@@ -170,6 +170,14 @@
     }
 }
 
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
+impl ::rand::distributions::Distribution<f64> for Hypergeometric {
+    fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> f64 {
+        rng.sample::<u64, _>(self) as f64
+    }
+}
+
 impl DiscreteCDF<u64, f64> for Hypergeometric {
     /// Calculates the cumulative distribution function for the hypergeometric
     /// distribution at `x`

src/distribution/multinomial.rs

@@ -159,6 +159,19 @@
     }
 }
 
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
+impl<D> ::rand::distributions::Distribution<OVector<u64, D>> for Multinomial<D>
+where
+    D: Dim,
+    nalgebra::DefaultAllocator: nalgebra::allocator::Allocator<f64, D>,
+    nalgebra::DefaultAllocator: nalgebra::allocator::Allocator<u64, D>,
+{
+    fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> OVector<u64, D> {
+        sample_generic(self, rng)
+    }
+}
+
 #[cfg(feature = "rand")]
 #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
 impl<D> ::rand::distributions::Distribution<OVector<f64, D>> for Multinomial<D>
@@ -167,17 +180,28 @@
     nalgebra::DefaultAllocator: nalgebra::allocator::Allocator<f64, D>,
 {
     fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> OVector<f64, D> {
-        use nalgebra::Const;
-
-        let p_cdf = super::categorical::prob_mass_to_cdf(self.p().as_slice());
-        let mut res = OVector::zeros_generic(self.p.shape_generic().0, Const::<1>);
-        for _ in 0..self.n {
-            let i = super::categorical::sample_unchecked(rng, &p_cdf);
-            let el = res.get_mut(i as usize).unwrap();
-            *el += 1.0;
-        }
-        res
+        sample_generic(self, rng)
+    }
+}
+
+#[cfg(feature = "rand")]
+fn sample_generic<D, R, T>(dist: &Multinomial<D>, rng: &mut R) -> OVector<T, D>
+where
+    D: Dim,
+    nalgebra::DefaultAllocator: nalgebra::allocator::Allocator<f64, D>,
+    nalgebra::DefaultAllocator: nalgebra::allocator::Allocator<T, D>,
+    R: ::rand::Rng + ?Sized,
+    T: ::num_traits::Num + ::nalgebra::Scalar + ::std::ops::AddAssign<T>,
+{
+    use nalgebra::Const;
+
+    let p_cdf = super::categorical::prob_mass_to_cdf(dist.p().as_slice());
+    let mut res = OVector::zeros_generic(dist.p.shape_generic().0, Const::<1>);
+    for _ in 0..dist.n {
+        let i = super::categorical::sample_unchecked(rng, &p_cdf);
+        res[i] += T::one();
     }
+    res
 }
 
 impl<D> MeanN<DVector<f64>> for Multinomial<D>

src/distribution/poisson.rs

@@ -89,6 +89,19 @@
     }
 }
 
+#[cfg(feature = "rand")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
+impl ::rand::distributions::Distribution<u64> for Poisson {
+    /// Generates one sample from the Poisson distribution either by
+    /// Knuth's method if lambda < 30.0 or Rejection method PA by
+    /// A. C. Atkinson from the Journal of the Royal Statistical Society
+    /// Series C (Applied Statistics) Vol. 28 No. 1. (1979) pp. 29 - 35
+    /// otherwise
+    fn sample<R: ::rand::Rng + ?Sized>(&self, rng: &mut R) -> u64 {
+        sample_unchecked(rng, self.lambda) as u64
+    }
+}
+
 #[cfg(feature = "rand")]
 #[cfg_attr(docsrs, doc(cfg(feature = "rand")))]
 impl ::rand::distributions::Distribution<f64> for Poisson {
@@ -279,6 +292,7 @@
         -self.lambda + x as f64 * self.lambda.ln() - factorial::ln_factorial(x)
     }
 }
+
 /// Generates one sample from the Poisson distribution either by
 /// Knuth's method if lambda < 30.0 or Rejection method PA by
 /// A. C. Atkinson from the Journal of the Royal Statistical Society