Adds squeeze() to dynamic arrays

src/impl_dyn.rs

@@ -11,7 +11,8 @@ use crate::imp_prelude::*;
 
 /// # Methods for Dynamic-Dimensional Arrays
 impl<A, S> ArrayBase<S, IxDyn>
-where S: Data<Elem = A>
+where
+    S: Data<Elem = A>,
 {
     /// Insert new array axis of length 1 at `axis`, modifying the shape and
     /// strides in-place.
@@ -29,8 +30,7 @@ where S: Data<Elem = A>
     /// assert_eq!(a.shape(), &[2, 1, 3]);
     /// ```
     #[track_caller]
-    pub fn insert_axis_inplace(&mut self, axis: Axis)
-    {
+    pub fn insert_axis_inplace(&mut self, axis: Axis) {
         assert!(axis.index() <= self.ndim());
         self.dim = self.dim.insert_axis(axis);
         self.strides = self.strides.insert_axis(axis);
@@ -52,10 +52,62 @@ where S: Data<Elem = A>
     /// assert_eq!(a.shape(), &[2]);
     /// ```
     #[track_caller]
-    pub fn index_axis_inplace(&mut self, axis: Axis, index: usize)
-    {
+    pub fn index_axis_inplace(&mut self, axis: Axis, index: usize) {
         self.collapse_axis(axis, index);
         self.dim = self.dim.remove_axis(axis);
         self.strides = self.strides.remove_axis(axis);
     }
+
+    /// Remove axes of length 1 and return the modified array.
+    ///
+    /// If the array has more the one dimension, the result array will always
+    /// have at least one dimension, even if it has a length of 1.
+    ///
+    /// ```
+    /// use ndarray::{arr1, arr2, arr3};
+    ///
+    /// let a = arr3(&[[[1, 2, 3]], [[4, 5, 6]]]).into_dyn();
+    /// assert_eq!(a.shape(), &[2, 1, 3]);
+    /// let b = a.squeeze();
+    /// assert_eq!(b, arr2(&[[1, 2, 3], [4, 5, 6]]).into_dyn());
+    /// assert_eq!(b.shape(), &[2, 3]);
+    ///
+    /// let c = arr2(&[[1]]).into_dyn();
+    /// assert_eq!(c.shape(), &[1, 1]);
+    /// let d = c.squeeze();
+    /// assert_eq!(d, arr1(&[1]).into_dyn());
+    /// assert_eq!(d.shape(), &[1]);
+    /// ```
+    #[track_caller]
+    pub fn squeeze(self) -> Self {
+        let mut out = self;
+        for axis in (0..out.shape().len()).rev() {
+            if out.shape()[axis] == 1 && out.shape().len() > 1 {
+                out = out.remove_axis(Axis(axis));
+            }
+        }
+        out
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{arr1, arr2, arr3};
+
+    #[test]
+    fn test_squeeze() {
+        let a = arr3(&[[[1, 2, 3]], [[4, 5, 6]]]).into_dyn();
+        assert_eq!(a.shape(), &[2, 1, 3]);
+
+        let b = a.squeeze();
+        assert_eq!(b, arr2(&[[1, 2, 3], [4, 5, 6]]).into_dyn());
+        assert_eq!(b.shape(), &[2, 3]);
+
+        let c = arr2(&[[1]]).into_dyn();
+        assert_eq!(c.shape(), &[1, 1]);
+
+        let d = c.squeeze();
+        assert_eq!(d, arr1(&[1]).into_dyn());
+        assert_eq!(d.shape(), &[1]);
+    }
 }