add fit_intercept to LASSO (#344)

georeth · web-flow · commit 18de2aa244d9 · 2025-11-29T02:46:14.000Z
* add fit_intercept to LASSO
* lasso: intercept=None if fit_intercept is false
* update CHANGELOG.md to reflect lasso changes
* lasso: minor
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+- WARNING: Breaking changes!
+- `LassoParameters` and `LassoSearchParameters` have a new field `fit_intercept`. When it is set to false, the `beta_0` term in the formula will be forced to zero, and `intercept` field in `Lasso` will be set to `None`.
+
+
 ## [0.4.0] - 2023-04-05
 
 ## Added
diff --git a/src/linear/elastic_net.rs b/src/linear/elastic_net.rs
@@ -345,6 +345,7 @@ impl<TX: FloatNumber + RealNumber, TY: Number, X: Array2<TX>, Y: Array1<TY>>
                 l1_reg * gamma,
                 parameters.max_iter,
                 TX::from_f64(parameters.tol).unwrap(),
+                true,
             )?;
 
             for i in 0..p {
@@ -371,6 +372,7 @@ impl<TX: FloatNumber + RealNumber, TY: Number, X: Array2<TX>, Y: Array1<TY>>
                 l1_reg * gamma,
                 parameters.max_iter,
                 TX::from_f64(parameters.tol).unwrap(),
+                true,
             )?;
 
             for i in 0..p {
diff --git a/src/linear/lasso.rs b/src/linear/lasso.rs
@@ -53,6 +53,9 @@ pub struct LassoParameters {
     #[cfg_attr(feature = "serde", serde(default))]
     /// The maximum number of iterations
     pub max_iter: usize,
+    #[cfg_attr(feature = "serde", serde(default))]
+    /// If false, force the intercept parameter (beta_0) to be zero.
+    pub fit_intercept: bool,
 }
 
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
@@ -86,6 +89,12 @@ impl LassoParameters {
         self.max_iter = max_iter;
         self
     }
+
+    /// If false, force the intercept parameter (beta_0) to be zero.
+    pub fn with_fit_intercept(mut self, fit_intercept: bool) -> Self {
+        self.fit_intercept = fit_intercept;
+        self
+    }
 }
 
 impl Default for LassoParameters {
@@ -95,6 +104,7 @@ impl Default for LassoParameters {
             normalize: true,
             tol: 1e-4,
             max_iter: 1000,
+            fit_intercept: true,
         }
     }
 }
@@ -118,8 +128,8 @@ impl<TX: FloatNumber + RealNumber, TY: Number, X: Array2<TX>, Y: Array1<TY>>
 {
     fn new() -> Self {
         Self {
-            coefficients: Option::None,
-            intercept: Option::None,
+            coefficients: None,
+            intercept: None,
             _phantom_ty: PhantomData,
             _phantom_y: PhantomData,
         }
@@ -155,6 +165,9 @@ pub struct LassoSearchParameters {
     #[cfg_attr(feature = "serde", serde(default))]
     /// The maximum number of iterations
     pub max_iter: Vec<usize>,
+    #[cfg_attr(feature = "serde", serde(default))]
+    /// The maximum number of iterations
+    pub fit_intercept: Vec<bool>,
 }
 
 /// Lasso grid search iterator
@@ -164,6 +177,7 @@ pub struct LassoSearchParametersIterator {
     current_normalize: usize,
     current_tol: usize,
     current_max_iter: usize,
+    current_fit_intercept: usize,
 }
 
 impl IntoIterator for LassoSearchParameters {
@@ -177,6 +191,7 @@ impl IntoIterator for LassoSearchParameters {
             current_normalize: 0,
             current_tol: 0,
             current_max_iter: 0,
+            current_fit_intercept: 0,
         }
     }
 }
@@ -189,6 +204,7 @@ impl Iterator for LassoSearchParametersIterator {
             && self.current_normalize == self.lasso_search_parameters.normalize.len()
             && self.current_tol == self.lasso_search_parameters.tol.len()
             && self.current_max_iter == self.lasso_search_parameters.max_iter.len()
+            && self.current_fit_intercept == self.lasso_search_parameters.fit_intercept.len()
         {
             return None;
         }
@@ -198,6 +214,7 @@ impl Iterator for LassoSearchParametersIterator {
             normalize: self.lasso_search_parameters.normalize[self.current_normalize],
             tol: self.lasso_search_parameters.tol[self.current_tol],
             max_iter: self.lasso_search_parameters.max_iter[self.current_max_iter],
+            fit_intercept: self.lasso_search_parameters.fit_intercept[self.current_fit_intercept],
         };
 
         if self.current_alpha + 1 < self.lasso_search_parameters.alpha.len() {
@@ -214,11 +231,19 @@ impl Iterator for LassoSearchParametersIterator {
             self.current_normalize = 0;
             self.current_tol = 0;
             self.current_max_iter += 1;
+        } else if self.current_fit_intercept + 1 < self.lasso_search_parameters.fit_intercept.len()
+        {
+            self.current_alpha = 0;
+            self.current_normalize = 0;
+            self.current_tol = 0;
+            self.current_max_iter = 0;
+            self.current_fit_intercept += 1;
         } else {
             self.current_alpha += 1;
             self.current_normalize += 1;
             self.current_tol += 1;
             self.current_max_iter += 1;
+            self.current_fit_intercept += 1;
         }
 
         Some(next)
@@ -234,6 +259,7 @@ impl Default for LassoSearchParameters {
             normalize: vec![default_params.normalize],
             tol: vec![default_params.tol],
             max_iter: vec![default_params.max_iter],
+            fit_intercept: vec![default_params.fit_intercept],
         }
     }
 }
@@ -283,19 +309,23 @@ impl<TX: FloatNumber + RealNumber, TY: Number, X: Array2<TX>, Y: Array1<TY>> Las
                 l1_reg,
                 parameters.max_iter,
                 TX::from_f64(parameters.tol).unwrap(),
+                parameters.fit_intercept,
             )?;
 
             for (j, col_std_j) in col_std.iter().enumerate().take(p) {
                 w[j] /= *col_std_j;
             }
 
-            let mut b = TX::zero();
+            let b = if parameters.fit_intercept {
+                let mut xw_mean = TX::zero();
+                for (i, col_mean_i) in col_mean.iter().enumerate().take(p) {
+                    xw_mean += w[i] * *col_mean_i;
+                }
 
-            for (i, col_mean_i) in col_mean.iter().enumerate().take(p) {
-                b += w[i] * *col_mean_i;
-            }
-
-            b = TX::from_f64(y.mean_by()).unwrap() - b;
+                Some(TX::from_f64(y.mean_by()).unwrap() - xw_mean)
+            } else {
+                None
+            };
             (X::from_column(&w), b)
         } else {
             let mut optimizer = InteriorPointOptimizer::new(x, p);
@@ -306,13 +336,21 @@ impl<TX: FloatNumber + RealNumber, TY: Number, X: Array2<TX>, Y: Array1<TY>> Las
                 l1_reg,
                 parameters.max_iter,
                 TX::from_f64(parameters.tol).unwrap(),
+                parameters.fit_intercept,
             )?;
 
-            (X::from_column(&w), TX::from_f64(y.mean_by()).unwrap())
+            (
+                X::from_column(&w),
+                if parameters.fit_intercept {
+                    Some(TX::from_f64(y.mean_by()).unwrap())
+                } else {
+                    None
+                },
+            )
         };
 
         Ok(Lasso {
-            intercept: Some(b),
+            intercept: b,
             coefficients: Some(w),
             _phantom_ty: PhantomData,
             _phantom_y: PhantomData,
@@ -378,30 +416,28 @@ mod tests {
         let parameters = LassoSearchParameters {
             alpha: vec![0., 1.],
             max_iter: vec![10, 100],
+            fit_intercept: vec![false, true],
             ..Default::default()
         };
-        let mut iter = parameters.into_iter();
-        let next = iter.next().unwrap();
-        assert_eq!(next.alpha, 0.);
-        assert_eq!(next.max_iter, 10);
-        let next = iter.next().unwrap();
-        assert_eq!(next.alpha, 1.);
-        assert_eq!(next.max_iter, 10);
-        let next = iter.next().unwrap();
-        assert_eq!(next.alpha, 0.);
-        assert_eq!(next.max_iter, 100);
-        let next = iter.next().unwrap();
-        assert_eq!(next.alpha, 1.);
-        assert_eq!(next.max_iter, 100);
+
+        let mut iter = parameters.clone().into_iter();
+        for current_fit_intercept in 0..parameters.fit_intercept.len() {
+            for current_max_iter in 0..parameters.max_iter.len() {
+                for current_alpha in 0..parameters.alpha.len() {
+                    let next = iter.next().unwrap();
+                    assert_eq!(next.alpha, parameters.alpha[current_alpha]);
+                    assert_eq!(next.max_iter, parameters.max_iter[current_max_iter]);
+                    assert_eq!(
+                        next.fit_intercept,
+                        parameters.fit_intercept[current_fit_intercept]
+                    );
+                }
+            }
+        }
         assert!(iter.next().is_none());
     }
 
-    #[cfg_attr(
-        all(target_arch = "wasm32", not(target_os = "wasi")),
-        wasm_bindgen_test::wasm_bindgen_test
-    )]
-    #[test]
-    fn lasso_fit_predict() {
+    fn get_example_x_y() -> (DenseMatrix<f64>, Vec<f64>) {
         let x = DenseMatrix::from_2d_array(&[
             &[234.289, 235.6, 159.0, 107.608, 1947., 60.323],
             &[259.426, 232.5, 145.6, 108.632, 1948., 61.122],
@@ -427,6 +463,17 @@ mod tests {
             114.2, 115.7, 116.9,
         ];
 
+        (x, y)
+    }
+
+    #[cfg_attr(
+        all(target_arch = "wasm32", not(target_os = "wasi")),
+        wasm_bindgen_test::wasm_bindgen_test
+    )]
+    #[test]
+    fn lasso_fit_predict() {
+        let (x, y) = get_example_x_y();
+
         let y_hat = Lasso::fit(&x, &y, Default::default())
             .and_then(|lr| lr.predict(&x))
             .unwrap();
@@ -441,6 +488,7 @@ mod tests {
                 normalize: false,
                 tol: 1e-4,
                 max_iter: 1000,
+                fit_intercept: true,
             },
         )
         .and_then(|lr| lr.predict(&x))
@@ -479,35 +527,46 @@ mod tests {
         assert!(mean_absolute_error(&w, &expected_w) < 1e-3); // actual mean_absolute_error is about 2e-4
     }
 
+    #[cfg_attr(
+        all(target_arch = "wasm32", not(target_os = "wasi")),
+        wasm_bindgen_test::wasm_bindgen_test
+    )]
+    #[test]
+    fn test_fit_intercept() {
+        let (x, y) = get_example_x_y();
+        let fit_result = Lasso::fit(
+            &x,
+            &y,
+            LassoParameters {
+                alpha: 0.1,
+                normalize: false,
+                tol: 1e-8,
+                max_iter: 1000,
+                fit_intercept: false,
+            },
+        )
+        .unwrap();
+
+        let w = fit_result.coefficients().iterator(0).copied().collect();
+        // by sklearn LassoLars. coordinate descent doesn't converge well
+        let expected_w = vec![
+            0.18335684,
+            0.02106526,
+            0.00703214,
+            -1.35952542,
+            0.09295222,
+            0.,
+        ];
+        assert!(mean_absolute_error(&w, &expected_w) < 1e-6);
+        assert_eq!(fit_result.intercept, None);
+    }
+
     // TODO: serialization for the new DenseMatrix needs to be implemented
     // #[cfg_attr(all(target_arch = "wasm32", not(target_os = "wasi")), wasm_bindgen_test::wasm_bindgen_test)]
     // #[test]
     // #[cfg(feature = "serde")]
     // fn serde() {
-    //     let x = DenseMatrix::from_2d_array(&[
-    //         &[234.289, 235.6, 159.0, 107.608, 1947., 60.323],
-    //         &[259.426, 232.5, 145.6, 108.632, 1948., 61.122],
-    //         &[258.054, 368.2, 161.6, 109.773, 1949., 60.171],
-    //         &[284.599, 335.1, 165.0, 110.929, 1950., 61.187],
-    //         &[328.975, 209.9, 309.9, 112.075, 1951., 63.221],
-    //         &[346.999, 193.2, 359.4, 113.270, 1952., 63.639],
-    //         &[365.385, 187.0, 354.7, 115.094, 1953., 64.989],
-    //         &[363.112, 357.8, 335.0, 116.219, 1954., 63.761],
-    //         &[397.469, 290.4, 304.8, 117.388, 1955., 66.019],
-    //         &[419.180, 282.2, 285.7, 118.734, 1956., 67.857],
-    //         &[442.769, 293.6, 279.8, 120.445, 1957., 68.169],
-    //         &[444.546, 468.1, 263.7, 121.950, 1958., 66.513],
-    //         &[482.704, 381.3, 255.2, 123.366, 1959., 68.655],
-    //         &[502.601, 393.1, 251.4, 125.368, 1960., 69.564],
-    //         &[518.173, 480.6, 257.2, 127.852, 1961., 69.331],
-    //         &[554.894, 400.7, 282.7, 130.081, 1962., 70.551],
-    //     ]);
-
-    //     let y = vec![
-    //         83.0, 88.5, 88.2, 89.5, 96.2, 98.1, 99.0, 100.0, 101.2, 104.6, 108.4, 110.8, 112.6,
-    //         114.2, 115.7, 116.9,
-    //     ];
-
+    //     let (x, y) = get_lasso_sample_x_y();
     //     let lr = Lasso::fit(&x, &y, Default::default()).unwrap();
 
     //     let deserialized_lr: Lasso<f64, f64, DenseMatrix<f64>, Vec<f64>> =
diff --git a/src/linear/lasso_optimizer.rs b/src/linear/lasso_optimizer.rs
@@ -45,6 +45,7 @@ impl<T: FloatNumber, X: Array2<T>> InteriorPointOptimizer<T, X> {
         lambda: T,
         max_iter: usize,
         tol: T,
+        fit_intercept: bool,
     ) -> Result<Vec<T>, Failed> {
         let (n, p) = x.shape();
         let p_f64 = T::from_usize(p).unwrap();
@@ -61,7 +62,11 @@ impl<T: FloatNumber, X: Array2<T>> InteriorPointOptimizer<T, X> {
         let mu = T::two();
 
         // let y = M::from_row_vector(y.sub_scalar(y.mean_by())).transpose();
-        let y = y.sub_scalar(T::from_f64(y.mean_by()).unwrap());
+        let y = if fit_intercept {
+            y.sub_scalar(T::from_f64(y.mean_by()).unwrap())
+        } else {
+            y.to_owned()
+        };
 
         let mut max_ls_iter = 100;
         let mut pitr = 0;
