fix: Baseline should signal its enablement through an index and not a…

… feature (#3069)

* fix: Baseline should signal its enablement through an index and not a feature

* formatting

* Update baseline_test.stderr

test/train-sets/ref/baseline_test.stderr

@@ -24,4 +24,4 @@ weighted label sum = 91.000000
 average loss = 0.190245
 best constant = 0.455000
 best constant's loss = 0.247975
-total feature number = 15482
+total feature number = 15482

vowpalwabbit/baseline.cc

@@ -2,6 +2,8 @@
 // individual contributors. All rights reserved. Released under a BSD (revised)
 // license as described in the file LICENSE.
 
+#include "baseline.h"
+
 #include <cfloat>
 #include <cerrno>
 
@@ -15,47 +17,25 @@ using namespace VW::config;
 namespace
 {
 const float max_multiplier = 1000.f;
-const size_t baseline_enabled_idx = 1357;  // feature index for enabling baseline
 }  // namespace
 
 namespace BASELINE
 {
 void set_baseline_enabled(example* ec)
 {
-  auto& fs = ec->feature_space[message_namespace];
-  for (auto& f : fs)
-  {
-    if (f.index() == baseline_enabled_idx)
-    {
-      f.value() = 1;
-      return;
-    }
-  }
-  // if not found, push new feature
-  fs.push_back(1, baseline_enabled_idx);
+  if (!baseline_enabled(ec)) { ec->indices.push_back(baseline_enabled_message_namespace); }
 }
 
 void reset_baseline_disabled(example* ec)
 {
-  auto& fs = ec->feature_space[message_namespace];
-  for (auto& f : fs)
-  {
-    if (f.index() == baseline_enabled_idx)
-    {
-      f.value() = 0;
-      return;
-    }
-  }
+  auto it = std::find(ec->indices.begin(), ec->indices.end(), baseline_enabled_message_namespace);
+  if (it != ec->indices.end()) { ec->indices.erase(it); }
 }
 
 bool baseline_enabled(example* ec)
 {
-  auto& fs = ec->feature_space[message_namespace];
-  for (auto& f : fs)
-  {
-    if (f.index() == baseline_enabled_idx) return f.value() == 1;
-  }
-  return false;
+  auto it = std::find(ec->indices.begin(), ec->indices.end(), baseline_enabled_message_namespace);
+  return it != ec->indices.end();
 }
 }  // namespace BASELINE
 

vowpalwabbit/constant.h

@@ -31,7 +31,7 @@ constexpr unsigned char spelling_namespace = 133;      // this is \x85
 constexpr unsigned char conditioning_namespace = 134;  // this is \x86
 constexpr unsigned char dictionary_namespace = 135;    // this is \x87
 constexpr unsigned char node_id_namespace = 136;       // this is \x88
-constexpr unsigned char message_namespace = 137;       // this is \x89
+constexpr unsigned char baseline_enabled_message_namespace = 137;  // this is \x89
 constexpr unsigned char ccb_slot_namespace = 139;
 constexpr unsigned char ccb_id_namespace = 140;