Add shuffle_axis_inplace and shuffle_axis_inplace_using

ndarray-rand/src/lib.rs

@@ -34,8 +34,7 @@ use crate::rand::rngs::SmallRng;
 use crate::rand::seq::index;
 use crate::rand::{thread_rng, Rng, SeedableRng};
 
-use ndarray::{Array, Axis, RemoveAxis, ShapeBuilder};
-use ndarray::{ArrayBase, DataOwned, Dimension};
+use ndarray::{Array, Axis, Data, DataMut, RemoveAxis, ShapeBuilder, ArrayBase, DataOwned, Dimension};
 #[cfg(feature = "quickcheck")]
 use quickcheck::{Arbitrary, Gen};
 
@@ -64,7 +63,7 @@ pub mod rand_distr {
 /// [`.random_using()`](#tymethod.random_using).
 pub trait RandomExt<S, A, D>
 where
-    S: DataOwned<Elem = A>,
+    S: Data<Elem = A>,
     D: Dimension,
 {
     /// Create an array with shape `dim` with elements drawn from
@@ -87,6 +86,7 @@ where
     /// # }
     fn random<Sh, IdS>(shape: Sh, distribution: IdS) -> ArrayBase<S, D>
     where
+        S: DataOwned<Elem=A>,
         IdS: Distribution<S::Elem>,
         Sh: ShapeBuilder<Dim = D>;
 
@@ -116,6 +116,7 @@ where
     /// # }
     fn random_using<Sh, IdS, R>(shape: Sh, distribution: IdS, rng: &mut R) -> ArrayBase<S, D>
     where
+        S: DataOwned<Elem=A>,
         IdS: Distribution<S::Elem>,
         R: Rng + ?Sized,
         Sh: ShapeBuilder<Dim = D>;
@@ -225,17 +226,93 @@ where
         R: Rng + ?Sized,
         A: Copy,
         D: RemoveAxis;
+
+    /// Shuffle `self`'s slices along `axis`.
+    ///
+    /// It uses [Fisher-Yates shuffling algorithm](https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle).
+    ///
+    /// ***Panics*** when creation of the RNG fails.
+    /// ```
+    /// use ndarray::{array, Axis};
+    /// use ndarray_rand::RandomExt;
+    ///
+    /// # fn main() {
+    /// let mut a = array![
+    ///     [1., 2., 3.],
+    ///     [4., 5., 6.],
+    ///     [7., 8., 9.],
+    ///     [10., 11., 12.],
+    /// ];
+    /// // Let's shuffle `a`'s columns!
+    /// // Shuffling modifies the array in place, nothing is returned
+    /// a.shuffle_axis_inplace(Axis(1));
+    /// println!("{:?}", a);
+    /// // Example Output:
+    /// // [
+    /// //   [1., 3., 2.],
+    /// //   [4., 6., 5.],
+    /// //   [7., 9., 8.],
+    /// //   [10., 12., 11.],
+    /// // ]
+    /// # }
+    /// ```
+    fn shuffle_axis_inplace(&mut self, axis: Axis)
+    where
+        D: RemoveAxis,
+        S: DataMut;
+
+    /// Shuffle `self`'s slices along `axis` using the specified random number generator `rng`.
+    ///
+    /// It uses [Fisher-Yates shuffling algorithm](https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle).
+    ///
+    /// ***Panics*** when creation of the RNG fails.
+    /// ```
+    /// use ndarray::{array, Axis};
+    /// use ndarray_rand::RandomExt;
+    /// use ndarray_rand::rand::SeedableRng;
+    /// use rand_isaac::isaac64::Isaac64Rng;
+    ///
+    /// # fn main() {
+    /// // Get a seeded random number generator for reproducibility (Isaac64 algorithm)
+    /// let seed = 42;
+    /// let mut rng = Isaac64Rng::seed_from_u64(seed);
+    ///
+    /// let mut a = array![
+    ///     [1., 2., 3.],
+    ///     [4., 5., 6.],
+    ///     [7., 8., 9.],
+    ///     [10., 11., 12.],
+    /// ];
+    /// // Let's shuffle `a`'s rows!
+    /// // Shuffling modifies the array in place, nothing is returned
+    /// a.shuffle_axis_inplace_using(Axis(0), &mut rng);
+    /// println!("{:?}", a);
+    /// // Example Output:
+    /// // [
+    /// //   [7., 8., 9.],
+    /// //   [4., 5., 6.],
+    /// //   [10., 11., 12.],
+    /// //   [1., 2., 3.],
+    /// // ]
+    /// # }
+    /// ```
+    fn shuffle_axis_inplace_using<R>(&mut self, axis: Axis, rng: &mut R)
+    where
+        R: Rng + ?Sized,
+        D: RemoveAxis,
+        S: DataMut;
 }
 
 impl<S, A, D> RandomExt<S, A, D> for ArrayBase<S, D>
 where
-    S: DataOwned<Elem = A>,
+    S: Data<Elem = A>,
     D: Dimension,
 {
     fn random<Sh, IdS>(shape: Sh, dist: IdS) -> ArrayBase<S, D>
     where
         IdS: Distribution<S::Elem>,
         Sh: ShapeBuilder<Dim = D>,
+        S: DataOwned<Elem=A>,
     {
         Self::random_using(shape, dist, &mut get_rng())
     }
@@ -245,6 +322,7 @@ where
         IdS: Distribution<S::Elem>,
         R: Rng + ?Sized,
         Sh: ShapeBuilder<Dim = D>,
+        S: DataOwned<Elem=A>,
     {
         Self::from_shape_fn(shape, |_| dist.sample(rng))
     }
@@ -280,6 +358,41 @@ where
         };
         self.select(axis, &indices)
     }
+
+    fn shuffle_axis_inplace(&mut self, axis: Axis)
+    where
+        D: RemoveAxis,
+        S: DataMut,
+    {
+        self.shuffle_axis_inplace_using(axis, &mut get_rng())
+    }
+
+    fn shuffle_axis_inplace_using<R>(&mut self, axis: Axis, rng: &mut R)
+    where
+        R: Rng + ?Sized,
+        D: RemoveAxis,
+        S: DataMut,
+    {
+        for i in (1..self.len_of(axis)).rev() {
+            // Invariant: elements with index > i have been locked in place.
+            let j = rng.gen_range(0, i + 1);
+
+            if i != j {
+                // Swap the two slices along `axis`
+                let slice1 = self.index_axis(axis, i);
+                let slice2 = self.index_axis(axis, j);
+
+                for (x, y) in slice1.iter().zip(slice2.iter()) {
+                    // Swap the two elements.
+                    let ptr1 = x as *const A as *mut A;
+                    let ptr2 = y as *const A as *mut A;
+                    unsafe {
+                        std::ptr::swap(ptr1, ptr2);
+                    }
+                }
+            }
+        }
+    }
 }
 
 /// Used as parameter in [`sample_axis`] and [`sample_axis_using`] to determine

ndarray-rand/tests/tests.rs

@@ -108,3 +108,20 @@ fn sampling_with_replacement_from_a_zero_length_axis_should_panic() {
     let a = Array::random((0, n), Uniform::new(0., 2.));
     let _samples = a.sample_axis(Axis(0), 1, SamplingStrategy::WithReplacement);
 }
+
+quickcheck! {
+    fn shuffling_works(m: usize, n: usize) -> bool {
+        let a = Array::random((m, n), Uniform::new(0., 2.));
+
+        // Get a clone of `a` and shuffle it in place
+        let mut results = vec![];
+        for &axis in &[Axis(0), Axis(1)] {
+            let mut b = a.clone();
+            b.shuffle_axis_inplace(axis);
+
+            let result = b.axis_iter(axis).all(|lane| is_subset(&a, &lane, axis));
+            results.push(result)
+        }
+        results.into_iter().all(|p| p)
+    }
+}