[REVIEW] Support for sample_weight parameter in LogisticRegression

cpp/include/cuml/linear_model/glm.hpp

@@ -124,12 +124,12 @@ void qnFit(const raft::handle_t &cuml_handle, float *X, float *y, int N, int D,
            int C, bool fit_intercept, float l1, float l2, int max_iter,
            float grad_tol, int linesearch_max_iter, int lbfgs_memory,
            int verbosity, float *w0, float *f, int *num_iters, bool X_col_major,
-           int loss_type);
+           int loss_type, float *sample_weight = nullptr);
 void qnFit(const raft::handle_t &cuml_handle, double *X, double *y, int N,
            int D, int C, bool fit_intercept, double l1, double l2, int max_iter,
            double grad_tol, int linesearch_max_iter, int lbfgs_memory,
            int verbosity, double *w0, double *f, int *num_iters,
-           bool X_col_major, int loss_type);
+           bool X_col_major, int loss_type, double *sample_weight = nullptr);
 /** @} */
 
 /**

cpp/src/glm/glm.cu

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, NVIDIA CORPORATION.
+ * Copyright (c) 2018-2021, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -71,20 +71,20 @@ void qnFit(const raft::handle_t &cuml_handle, float *X, float *y, int N, int D,
            int C, bool fit_intercept, float l1, float l2, int max_iter,
            float grad_tol, int linesearch_max_iter, int lbfgs_memory,
            int verbosity, float *w0, float *f, int *num_iters, bool X_col_major,
-           int loss_type) {
+           int loss_type, float *sample_weight) {
   qnFit(cuml_handle, X, y, N, D, C, fit_intercept, l1, l2, max_iter, grad_tol,
         linesearch_max_iter, lbfgs_memory, verbosity, w0, f, num_iters,
-        X_col_major, loss_type, cuml_handle.get_stream());
+        X_col_major, loss_type, cuml_handle.get_stream(), sample_weight);
 }
 
 void qnFit(const raft::handle_t &cuml_handle, double *X, double *y, int N,
            int D, int C, bool fit_intercept, double l1, double l2, int max_iter,
            double grad_tol, int linesearch_max_iter, int lbfgs_memory,
            int verbosity, double *w0, double *f, int *num_iters,
-           bool X_col_major, int loss_type) {
+           bool X_col_major, int loss_type, double *sample_weight) {
   qnFit(cuml_handle, X, y, N, D, C, fit_intercept, l1, l2, max_iter, grad_tol,
         linesearch_max_iter, lbfgs_memory, verbosity, w0, f, num_iters,
-        X_col_major, loss_type, cuml_handle.get_stream());
+        X_col_major, loss_type, cuml_handle.get_stream(), sample_weight);
 }
 
 void qnDecisionFunction(const raft::handle_t &cuml_handle, float *X, int N,

cpp/src/glm/qn/glm_base.cuh

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, NVIDIA CORPORATION.
+ * Copyright (c) 2018-2021, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,7 @@
 #include <raft/cuda_utils.cuh>
 #include <raft/linalg/add.cuh>
 #include <raft/linalg/binary_op.cuh>
+#include <raft/linalg/map.cuh>
 #include <raft/linalg/map_then_reduce.cuh>
 #include <raft/linalg/matrix_vector_op.cuh>
 #include <raft/stats/mean.cuh>
@@ -96,9 +97,22 @@ struct GLMBase : GLMDims {
   typedef SimpleVec<T> Vec;
 
   const raft::handle_t &handle;
+  T *sample_weights;
+  T weights_sum;
 
   GLMBase(const raft::handle_t &handle, int D, int C, bool fit_intercept)
-    : GLMDims(C, D, fit_intercept), handle(handle) {}
+    : GLMDims(C, D, fit_intercept),
+      handle(handle),
+      sample_weights(nullptr),
+      weights_sum(0) {}
+
+  void add_sample_weights(T *sample_weights, int n_samples,
+                          cudaStream_t stream) {
+    this->sample_weights = sample_weights;
+    this->weights_sum =
+      thrust::reduce(thrust::cuda::par.on(stream), sample_weights,
+                     sample_weights + n_samples, (T)0, thrust::plus<T>());
+  }
 
   /*
    * Computes the following:
@@ -111,22 +125,36 @@ struct GLMBase : GLMDims {
                            cudaStream_t stream) {
     // Base impl assumes simple case C = 1
     Loss *loss = static_cast<Loss *>(this);
-    T invN = 1.0 / y.len;
-
-    auto f_l = [=] __device__(const T y, const T z) {
-      return loss->lz(y, z) * invN;
-    };
 
     // TODO would be nice to have a kernel that fuses these two steps
     // This would be easy, if mapThenSumReduce allowed outputing the result of
     // map (supporting inplace)
-    raft::linalg::mapThenSumReduce(loss_val, y.len, f_l, stream, y.data,
-                                   Z.data);
-
-    auto f_dl = [=] __device__(const T y, const T z) {
-      return loss->dlz(y, z);
-    };
-    raft::linalg::binaryOp(Z.data, y.data, Z.data, y.len, f_dl, stream);
+    if (this->sample_weights) {  // Sample weights are in use
+      T normalization = 1.0 / this->weights_sum;
+      auto f_l = [=] __device__(const T y, const T z, const T weight) {
+        return loss->lz(y, z) * (weight * normalization);
+      };
+      raft::linalg::mapThenSumReduce(loss_val, y.len, f_l, stream, y.data,
+                                     Z.data, sample_weights);
+
+      auto f_dl = [=] __device__(const T y, const T z, const T weight) {
+        return weight * loss->dlz(y, z);
+      };
+      raft::linalg::map(Z.data, y.len, f_dl, stream, y.data, Z.data,
+                        sample_weights);
+    } else {  // Sample weights are not used
+      T normalization = 1.0 / y.len;
+      auto f_l = [=] __device__(const T y, const T z) {
+        return loss->lz(y, z) * normalization;
+      };
+      raft::linalg::mapThenSumReduce(loss_val, y.len, f_l, stream, y.data,
+                                     Z.data);
+
+      auto f_dl = [=] __device__(const T y, const T z) {
+        return loss->dlz(y, z);
+      };
+      raft::linalg::binaryOp(Z.data, y.data, Z.data, y.len, f_dl, stream);
+    }
   }
 
   inline void loss_grad(T *loss_val, Mat &G, const Mat &W,

cpp/src/glm/qn/qn.cuh

@@ -64,7 +64,7 @@ void qnFit(const raft::handle_t &handle, T *X, T *y, int N, int D, int C,
            bool fit_intercept, T l1, T l2, int max_iter, T grad_tol,
            int linesearch_max_iter, int lbfgs_memory, int verbosity, T *w0,
            T *f, int *num_iters, bool X_col_major, int loss_type,
-           cudaStream_t stream) {
+           cudaStream_t stream, T *sample_weight = nullptr) {
   STORAGE_ORDER ord = X_col_major ? COL_MAJOR : ROW_MAJOR;
   int C_len = (loss_type == 0) ? (C - 1) : C;
 
@@ -75,20 +75,23 @@ void qnFit(const raft::handle_t &handle, T *X, T *y, int N, int D, int C,
     case 0: {
       ASSERT(C == 2, "qn.h: logistic loss invalid C");
       LogisticLoss<T> loss(handle, D, fit_intercept);
+      if (sample_weight) loss.add_sample_weights(sample_weight, N, stream);
       qn_fit<T, decltype(loss)>(handle, loss, X, y, z.data, N, l1, l2, max_iter,
                                 grad_tol, linesearch_max_iter, lbfgs_memory,
                                 verbosity, w0, f, num_iters, ord, stream);
     } break;
     case 1: {
       ASSERT(C == 1, "qn.h: squared loss invalid C");
       SquaredLoss<T> loss(handle, D, fit_intercept);
+      if (sample_weight) loss.add_sample_weights(sample_weight, N, stream);
       qn_fit<T, decltype(loss)>(handle, loss, X, y, z.data, N, l1, l2, max_iter,
                                 grad_tol, linesearch_max_iter, lbfgs_memory,
                                 verbosity, w0, f, num_iters, ord, stream);
     } break;
     case 2: {
       ASSERT(C > 2, "qn.h: softmax invalid C");
       Softmax<T> loss(handle, D, C, fit_intercept);
+      if (sample_weight) loss.add_sample_weights(sample_weight, N, stream);
       qn_fit<T, decltype(loss)>(handle, loss, X, y, z.data, N, l1, l2, max_iter,
                                 grad_tol, linesearch_max_iter, lbfgs_memory,
                                 verbosity, w0, f, num_iters, ord, stream);

python/cuml/linear_model/logistic_regression.pyx

@@ -16,6 +16,7 @@
 
 # distutils: language = c++
 
+import numpy as np
 import cupy as cp
 import pprint
 
@@ -126,6 +127,15 @@ class LogisticRegression(Base,
        If False, the model expects that you have centered the data.
     class_weight: None
         Custom class weighs are currently not supported.
+    class_weight: dict or 'balanced', default=None
+        By default all classes have a weight one. However, a dictionary
+        can be provided with weights associated with classes
+        in the form ``{class_label: weight}``. The "balanced" mode
+        uses the values of y to automatically adjust weights
+        inversely proportional to class frequencies in the input data
+        as ``n_samples / (n_classes * np.bincount(y))``. Note that
+        these weights will be multiplied with sample_weight
+        (passed through the fit method) if sample_weight is specified.
     max_iter: int (default = 1000)
         Maximum number of iterations taken for the solvers to converge.
     linesearch_max_iter: int (default = 50)
@@ -178,6 +188,8 @@ class LogisticRegression(Base,
     """
 
     classes_ = CumlArrayDescriptor()
+    class_weight_ = CumlArrayDescriptor()
+    expl_spec_weights_ = CumlArrayDescriptor()
 
     def __init__(
         self,
@@ -199,9 +211,6 @@ class LogisticRegression(Base,
             handle=handle, verbose=verbose, output_type=output_type
         )
 
-        if class_weight:
-            raise ValueError("`class_weight` not supported.")
-
         if penalty not in supported_penalties:
             raise ValueError("`penalty` " + str(penalty) + "not supported.")
 
@@ -246,6 +255,21 @@ class LogisticRegression(Base,
 
         loss = "sigmoid"
 
+        if class_weight is not None:
+            if class_weight == 'balanced':
+                self.class_weight_ = 'balanced'
+            else:
+                classes = list(class_weight.keys())
+                weights = list(class_weight.values())
+                max_class = sorted(classes)[-1]
+                class_weight = cp.ones(max_class + 1)
+                class_weight[classes] = weights
+                self.class_weight_, _, _, _ = input_to_cuml_array(class_weight)
+                self.expl_spec_weights_, _, _, _ = \
+                    input_to_cuml_array(np.array(classes))
+        else:
+            self.class_weight_ = None
+
         self.solver_model = QN(
             loss=loss,
             fit_intercept=self.fit_intercept,
@@ -267,19 +291,63 @@ class LogisticRegression(Base,
 
     @generate_docstring()
     @cuml.internals.api_base_return_any(set_output_dtype=True)
-    def fit(self, X, y, convert_dtype=True) -> "LogisticRegression":
+    def fit(self, X, y, sample_weight=None,
+            convert_dtype=True) -> "LogisticRegression":
         """
         Fit the model with X and y.
 
         """
         # Converting y to device array here to use `unique` function
         # since calling input_to_cuml_array again in QN has no cost
         # Not needed to check dtype since qn class checks it already
-        y_m, _, _, _ = input_to_cuml_array(y)
-
+        y_m, n_rows, _, _ = input_to_cuml_array(y)
         self.classes_ = cp.unique(y_m)
         self._num_classes = len(self.classes_)
 
+        if self._num_classes == 2:
+            if self.classes_[0] != 0 or self.classes_[1] != 1:
+                raise ValueError("Only values of 0 and 1 are"
+                                 " supported for binary classification.")
+
+        if sample_weight is not None or self.class_weight_ is not None:
+            if sample_weight is None:
+                sample_weight = cp.ones(n_rows)
+
+            sample_weight, n_weights, D, _ = input_to_cuml_array(sample_weight)
+
+            if n_rows != n_weights or D != 1:
+                raise ValueError("sample_weight.shape == {}, "
+                                 "expected ({},)!".format(sample_weight.shape,
+                                                          n_rows))
+
+            def check_expl_spec_weights():
+                with cuml.using_output_type("numpy"):
+                    for c in self.expl_spec_weights_:
+                        i = np.searchsorted(self.classes_, c)
+                        if i >= self._num_classes or self.classes_[i] != c:
+                            msg = "Class label {} not present.".format(c)
+                            raise ValueError(msg)
+
+            if self.class_weight_ is not None:
+                if self.class_weight_ == 'balanced':
+                    class_weight = n_rows / \
+                                   (self._num_classes *
+                                    cp.bincount(y_m.to_output('cupy')))
+                    class_weight = CumlArray(class_weight)
+                else:
+                    check_expl_spec_weights()
+                    n_explicit = self.class_weight_.shape[0]
+                    if n_explicit != self._num_classes:
+                        class_weight = cp.ones(self._num_classes)
+                        class_weight[:n_explicit] = self.class_weight_
+                        class_weight = CumlArray(class_weight)
+                        self.class_weight_ = class_weight
+                    else:
+                        class_weight = self.class_weight_
+                out = y_m.to_output('cupy')
+                sample_weight *= class_weight[out].to_output('cupy')
+                sample_weight = CumlArray(sample_weight)
+
         if self._num_classes > 2:
             loss = "softmax"
         else:
@@ -293,7 +361,8 @@ class LogisticRegression(Base,
         if logger.should_log_for(logger.level_debug):
             logger.debug(self.verb_prefix + "Calling QN fit " + str(loss))
 
-        self.solver_model.fit(X, y_m, convert_dtype=convert_dtype)
+        self.solver_model.fit(X, y_m, sample_weight=sample_weight,
+                              convert_dtype=convert_dtype)
 
         # coefficients and intercept are contained in the same array
         if logger.should_log_for(logger.level_debug):

python/cuml/solvers/qn.pyx

@@ -53,7 +53,8 @@ cdef extern from "cuml/linear_model/glm.hpp" namespace "ML::GLM":
                float *f,
                int *num_iters,
                bool X_col_major,
-               int loss_type) except +
+               int loss_type,
+               float *sample_weight) except +
 
     void qnFit(handle_t& cuml_handle,
                double *X,
@@ -73,7 +74,8 @@ cdef extern from "cuml/linear_model/glm.hpp" namespace "ML::GLM":
                double *f,
                int *num_iters,
                bool X_col_major,
-               int loss_type) except +
+               int loss_type,
+               double *sample_weight) except +
 
     void qnDecisionFunction(handle_t& cuml_handle,
                             float *X,
@@ -291,7 +293,7 @@ class QN(Base,
             return self._coef_
 
     @generate_docstring()
-    def fit(self, X, y, convert_dtype=False) -> "QN":
+    def fit(self, X, y, sample_weight=None, convert_dtype=False) -> "QN":
         """
         Fit the model with X and y.
 
@@ -310,14 +312,25 @@ class QN(Base,
 
         self._num_classes = len(cp.unique(y_m))
 
+        cdef uintptr_t sample_weight_ptr = 0
+        if sample_weight is not None:
+            sample_weight, _, _, _ = \
+                input_to_cuml_array(sample_weight,
+                                    check_dtype=self.dtype,
+                                    check_rows=n_rows, check_cols=1,
+                                    convert_to_dtype=(self.dtype
+                                                      if convert_dtype
+                                                      else None))
+            sample_weight_ptr = sample_weight.ptr
+
         self.loss_type = self._get_loss_int(self.loss)
         if self.loss_type != 2 and self._num_classes > 2:
             raise ValueError("Only softmax (multinomial) loss supports more"
                              "than 2 classes.")
 
         if self.loss_type == 2 and self._num_classes <= 2:
-            raise ValueError("Only softmax (multinomial) loss supports more"
-                             "than 2 classes.")
+            raise ValueError("Two classes or less cannot be trained"
+                             "with softmax (multinomial).")
 
         if self.loss_type == 0:
             self._num_classes_dim = self._num_classes - 1
@@ -357,7 +370,8 @@ class QN(Base,
                   <float*> &objective32,
                   <int*> &num_iters,
                   <bool> True,
-                  <int> self.loss_type)
+                  <int> self.loss_type,
+                  <float*>sample_weight_ptr)
 
             self.objective = objective32
 
@@ -380,7 +394,8 @@ class QN(Base,
                   <double*> &objective64,
                   <int*> &num_iters,
                   <bool> True,
-                  <int> self.loss_type)
+                  <int> self.loss_type,
+                  <double*>sample_weight_ptr)
 
             self.objective = objective64