CSR row access and iterators

nalgebra-sparse/src/csr.rs

@@ -3,12 +3,17 @@ use crate::iter::SparsityPatternIter;
 
 use std::sync::Arc;
 use std::slice::{IterMut, Iter};
+use std::ops::Range;
+use num_traits::Zero;
+use std::ptr::slice_from_raw_parts_mut;
 
 /// A CSR representation of a sparse matrix.
 ///
 /// The Compressed Row Storage (CSR) format is well-suited as a general-purpose storage format
 /// for many sparse matrix applications.
 ///
+/// TODO: Storage explanation and examples
+///
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct CsrMatrix<T> {
     // Rows are major, cols are minor in the sparsity pattern
@@ -151,8 +156,103 @@ impl<T> CsrMatrix<T> {
             values_mut_iter: self.values.iter_mut()
         }
     }
+
+    /// Return the row at the given row index.
+    ///
+    /// Panics
+    /// ------
+    /// Panics if row index is out of bounds.
+    #[inline]
+    pub fn row(&self, index: usize) -> CsrRow<T> {
+        self.get_row(index)
+            .expect("Row index must be in bounds")
     }
 
+    /// Mutable row access for the given row index.
+    ///
+    /// Panics
+    /// ------
+    /// Panics if row index is out of bounds.
+    #[inline]
+    pub fn row_mut(&mut self, index: usize) -> CsrRowMut<T> {
+        self.get_row_mut(index)
+            .expect("Row index must be in bounds")
+    }
+
+    /// Return the row at the given row index, or `None` if out of bounds.
+    #[inline]
+    pub fn get_row(&self, index: usize) -> Option<CsrRow<T>> {
+        let range = self.get_index_range(index)?;
+        Some(CsrRow {
+            col_indices: &self.sparsity_pattern.minor_indices()[range.clone()],
+            values: &self.values[range],
+            ncols: self.ncols()
+        })
+    }
+
+    /// Mutable row access for the given row index, or `None` if out of bounds.
+    #[inline]
+    pub fn get_row_mut(&mut self, index: usize) -> Option<CsrRowMut<T>> {
+        let range = self.get_index_range(index)?;
+        Some(CsrRowMut {
+            ncols: self.ncols(),
+            col_indices: &self.sparsity_pattern.minor_indices()[range.clone()],
+            values: &mut self.values[range]
+        })
+    }
+
+    /// Internal method for simplifying access to a row's data.
+    fn get_index_range(&self, row_index: usize) -> Option<Range<usize>> {
+        let row_begin = *self.sparsity_pattern.major_offsets().get(row_index)?;
+        let row_end = *self.sparsity_pattern.major_offsets().get(row_index + 1)?;
+        Some(row_begin .. row_end)
+    }
+
+    /// An iterator over rows in the matrix.
+    pub fn row_iter(&self) -> CsrRowIter<T> {
+        CsrRowIter {
+            current_row_idx: 0,
+            matrix: self
+        }
+    }
+
+    /// A mutable iterator over rows in the matrix.
+    pub fn row_iter_mut(&mut self) -> CsrRowIterMut<T> {
+        CsrRowIterMut {
+            current_row_idx: 0,
+            pattern: &self.sparsity_pattern,
+            remaining_values: self.values.as_mut_ptr()
+        }
+    }
+}
+
+impl<T: Clone + Zero> CsrMatrix<T> {
+    /// Return the value in the matrix at the given global row/col indices, or `None` if out of
+    /// bounds.
+    ///
+    /// If the indices are in bounds, but no explicitly stored entry is associated with it,
+    /// `T::zero()` is returned. Note that this methods offers no way of distinguishing
+    /// explicitly stored zero entries from zero values that are only implicitly represented.
+    ///
+    /// Each call to this function incurs the cost of a binary search among the explicitly
+    /// stored column entries for the given row.
+    #[inline]
+    pub fn get(&self, row_index: usize, col_index: usize) -> Option<T> {
+        self.get_row(row_index)?.get(col_index)
+    }
+
+    /// Same as `get`, but panics if indices are out of bounds.
+    ///
+    /// Panics
+    /// ------
+    /// Panics if either index is out of bounds.
+    #[inline]
+    pub fn index(&self, row_index: usize, col_index: usize) -> T {
+        self.get(row_index, col_index).unwrap()
+    }
+}
+
+/// Iterator type for iterating over triplets in a CSR matrix.
 #[derive(Debug)]
 pub struct CsrTripletIter<'a, T> {
     pattern_iter: SparsityPatternIter<'a>,
@@ -173,6 +273,7 @@ impl<'a, T> Iterator for CsrTripletIter<'a, T> {
     }
 }
 
+/// Iterator type for mutably iterating over triplets in a CSR matrix.
 #[derive(Debug)]
 pub struct CsrTripletIterMut<'a, T> {
     pattern_iter: SparsityPatternIter<'a>,
@@ -193,3 +294,148 @@ impl<'a, T> Iterator for CsrTripletIterMut<'a, T> {
         }
     }
 }
+
+/// An immutable representation of a row in a CSR matrix.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CsrRow<'a, T> {
+    ncols: usize,
+    col_indices: &'a [usize],
+    values: &'a [T],
+}
+
+/// A mutable representation of a row in a CSR matrix.
+///
+/// Note that only explicitly stored entries can be mutated. The sparsity pattern belonging
+/// to the row cannot be modified.
+#[derive(Debug, PartialEq, Eq)]
+pub struct CsrRowMut<'a, T> {
+    ncols: usize,
+    col_indices: &'a [usize],
+    values: &'a mut [T]
+}
+
+/// Implement the methods common to both CsrRow and CsrRowMut
+macro_rules! impl_csr_row_common_methods {
+    ($name:ty) => {
+        impl<'a, T> $name {
+            /// The number of global columns in the row.
+            #[inline]
+            pub fn ncols(&self) -> usize {
+                self.ncols
+            }
+
+            /// The number of non-zeros in this row.
+            #[inline]
+            pub fn nnz(&self) -> usize {
+                self.col_indices.len()
+            }
+
+            /// The column indices corresponding to explicitly stored entries in this row.
+            #[inline]
+            pub fn col_indices(&self) -> &[usize] {
+                self.col_indices
+            }
+
+            /// The values corresponding to explicitly stored entries in this row.
+            #[inline]
+            pub fn values(&self) -> &[T] {
+                self.values
+            }
+        }
+
+        impl<'a, T: Clone + Zero> $name {
+            /// Return the value in the matrix at the given global column index, or `None` if out of
+            /// bounds.
+            ///
+            /// If the index is in bounds, but no explicitly stored entry is associated with it,
+            /// `T::zero()` is returned. Note that this methods offers no way of distinguishing
+            /// explicitly stored zero entries from zero values that are only implicitly represented.
+            ///
+            /// Each call to this function incurs the cost of a binary search among the explicitly
+            /// stored column entries for the current row.
+            pub fn get(&self, global_col_index: usize) -> Option<T> {
+                let local_index = self.col_indices().binary_search(&global_col_index);
+                if let Ok(local_index) = local_index {
+                    Some(self.values[local_index].clone())
+                } else if global_col_index < self.ncols {
+                    Some(T::zero())
+                } else {
+                    None
+                }
+            }
+        }
+    }
+}
+
+impl_csr_row_common_methods!(CsrRow<'a, T>);
+impl_csr_row_common_methods!(CsrRowMut<'a, T>);
+
+impl<'a, T> CsrRowMut<'a, T> {
+    /// Mutable access to the values corresponding to explicitly stored entries in this row.
+    pub fn values_mut(&mut self) -> &mut [T] {
+        self.values
+    }
+
+    /// Provides simultaneous access to column indices and mutable values corresponding to the
+    /// explicitly stored entries in this row.
+    ///
+    /// This method primarily facilitates low-level access for methods that process data stored
+    /// in CSR format directly.
+    pub fn cols_and_values_mut(&mut self) -> (&[usize], &mut [T]) {
+        (self.col_indices, self.values)
+    }
+}
+
+pub struct CsrRowIter<'a, T> {
+    // The index of the row that will be returned on the next
+    current_row_idx: usize,
+    matrix: &'a CsrMatrix<T>
+}
+
+impl<'a, T> Iterator for CsrRowIter<'a, T> {
+    type Item = CsrRow<'a, T>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let row = self.matrix.get_row(self.current_row_idx);
+        self.current_row_idx += 1;
+        row
+    }
+}
+
+pub struct CsrRowIterMut<'a, T> {
+    current_row_idx: usize,
+    pattern: &'a SparsityPattern,
+    remaining_values: *mut T,
+}
+
+impl<'a, T> Iterator for CsrRowIterMut<'a, T>
+where
+    T: 'a
+{
+    type Item = CsrRowMut<'a, T>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let lane = self.pattern.lane(self.current_row_idx);
+        let ncols = self.pattern.minor_dim();
+
+        if let Some(col_indices) = lane {
+            let count = col_indices.len();
+
+            // Note: I can't think of any way to construct this iterator without unsafe.
+            let values_in_row;
+            unsafe {
+                values_in_row = &mut *slice_from_raw_parts_mut(self.remaining_values, count);
+                self.remaining_values = self.remaining_values.add(count);
+            }
+            self.current_row_idx += 1;
+
+            Some(CsrRowMut {
+                ncols,
+                col_indices,
+                values: values_in_row
+            })
+        } else {
+            None
+        }
+    }
+}

nalgebra-sparse/src/lib.rs

@@ -1,3 +1,13 @@
+//! Sparse matrices and algorithms for nalgebra.
+//!
+//! TODO: Docs
+#![deny(non_camel_case_types)]
+#![deny(unused_parens)]
+#![deny(non_upper_case_globals)]
+#![deny(unused_qualifications)]
+#![deny(unused_results)]
+#![deny(missing_docs)]
+
 mod coo;
 mod csr;
 mod pattern;
@@ -5,7 +15,7 @@ mod pattern;
 pub mod ops;
 
 pub use coo::CooMatrix;
-pub use csr::CsrMatrix;
+pub use csr::{CsrMatrix, CsrRow, CsrRowMut};
 pub use pattern::{SparsityPattern};
 
 /// Iterator types for matrices.
@@ -25,6 +35,7 @@ pub mod iter {
 use std::error::Error;
 use std::fmt;
 
+/// Errors produced by functions that expect well-formed sparse format data.
 #[derive(Debug)]
 #[non_exhaustive]
 pub enum SparseFormatError {

nalgebra-sparse/src/pattern.rs

@@ -105,6 +105,7 @@ impl SparsityPattern {
     }
 }
 
+/// Iterator type for iterating over entries in a sparsity pattern.
 #[derive(Debug, Clone)]
 pub struct SparsityPatternIter<'a> {
     // See implementation of Iterator::next for an explanation of how these members are used