From 7352b8c0d4ee1df2115d7f79c1b9a4b6eca7e467 Mon Sep 17 00:00:00 2001
From: julianknodt <julianknodt@gmail.com>
Date: Sat, 16 Sep 2023 00:13:07 -0700
Subject: [PATCH] Add CscBuilder

For partial construction of Csc matrices
---
 nalgebra-sparse/src/cs.rs      | 22 +++++++++++++++++++++-
 nalgebra-sparse/src/csc.rs     | 21 +++++++++++++++++++--
 nalgebra-sparse/src/lib.rs     |  2 +-
 nalgebra-sparse/src/pattern.rs |  4 ++--
 4 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/nalgebra-sparse/src/cs.rs b/nalgebra-sparse/src/cs.rs
index e000e2de5..63f9bf0ab 100644
--- a/nalgebra-sparse/src/cs.rs
+++ b/nalgebra-sparse/src/cs.rs
@@ -5,7 +5,7 @@ use num_traits::One;
 
 use nalgebra::Scalar;
 
-use crate::pattern::SparsityPattern;
+use crate::pattern::{BuilderInsertError, SparsityPattern, SparsityPatternBuilder};
 use crate::utils::{apply_permutation, compute_sort_permutation};
 use crate::{SparseEntry, SparseEntryMut, SparseFormatError, SparseFormatErrorKind};
 
@@ -692,3 +692,23 @@ where
 
     Ok(())
 }
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CsBuilder<T> {
+    sparsity_builder: SparsityPatternBuilder,
+    values: Vec<T>,
+}
+
+impl<T> CsBuilder<T> {
+    pub fn new(major_dim: usize, minor_dim: usize) -> Self {
+        Self {
+            sparsity_builder: SparsityPatternBuilder::new(major_dim, minor_dim),
+            values: vec![],
+        }
+    }
+    pub fn insert(&mut self, maj: usize, min: usize, val: T) -> Result<(), BuilderInsertError> {
+        self.sparsity_builder.insert(maj, min)?;
+        self.values.push(val);
+        Ok(())
+    }
+}
diff --git a/nalgebra-sparse/src/csc.rs b/nalgebra-sparse/src/csc.rs
index 59823b3ca..2b39d106d 100644
--- a/nalgebra-sparse/src/csc.rs
+++ b/nalgebra-sparse/src/csc.rs
@@ -7,9 +7,11 @@
 mod csc_serde;
 
 use crate::cs;
-use crate::cs::{CsLane, CsLaneIter, CsLaneIterMut, CsLaneMut, CsMatrix};
+use crate::cs::{CsBuilder, CsLane, CsLaneIter, CsLaneIterMut, CsLaneMut, CsMatrix};
 use crate::csr::CsrMatrix;
-use crate::pattern::{SparsityPattern, SparsityPatternFormatError, SparsityPatternIter};
+use crate::pattern::{
+    BuilderInsertError, SparsityPattern, SparsityPatternFormatError, SparsityPatternIter,
+};
 use crate::{SparseEntry, SparseEntryMut, SparseFormatError, SparseFormatErrorKind};
 
 use nalgebra::{RealField, Scalar};
@@ -925,3 +927,18 @@ where
         self.lane_iter.next().map(|lane| CscColMut { lane })
     }
 }
+
+/// An incremental builder for a Csc matrix.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CscBuilder<T>(CsBuilder<T>);
+
+impl<T> CscBuilder<T> {
+    /// Constructs a new instance of a Csc Builder.
+    pub fn new(rows: usize, cols: usize) -> Self {
+        Self(CsBuilder::new(cols, rows))
+    }
+    /// Inserts a value into the builder. Must be called in ascending col, row order.
+    pub fn insert(&mut self, row: usize, col: usize, val: T) -> Result<(), BuilderInsertError> {
+        self.0.insert(col, row, val)
+    }
+}
diff --git a/nalgebra-sparse/src/lib.rs b/nalgebra-sparse/src/lib.rs
index fc12509e7..4988a8e85 100644
--- a/nalgebra-sparse/src/lib.rs
+++ b/nalgebra-sparse/src/lib.rs
@@ -171,7 +171,7 @@ use std::error::Error;
 use std::fmt;
 
 pub use self::coo::CooMatrix;
-pub use self::csc::CscMatrix;
+pub use self::csc::{CscBuilder, CscMatrix};
 pub use self::csr::CsrMatrix;
 
 /// Errors produced by functions that expect well-formed sparse format data.
diff --git a/nalgebra-sparse/src/pattern.rs b/nalgebra-sparse/src/pattern.rs
index 3440cfff0..549abe342 100644
--- a/nalgebra-sparse/src/pattern.rs
+++ b/nalgebra-sparse/src/pattern.rs
@@ -358,13 +358,13 @@ impl SparsityPattern {
 /// It requires elements to be added in sorted order. Specifically,
 /// For each element the major must be >= the previous element's major.
 /// If the major is the same, the minor must be in ascending order.
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub struct SparsityPatternBuilder {
     buf: SparsityPattern,
     major_dim: usize,
 }
 
-///
+/// An error when adding into the SparsityPatternBuilder
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub enum BuilderInsertError {
     ///