fix all negative values in cat features (#1547)

* fix all negative values in cat features

* fix a bug

src/io/bin.cpp

@@ -316,6 +316,9 @@ namespace LightGBM {
           }
         }
       }
+      num_bin_ = 0;
+      int rest_cnt = total_sample_cnt - na_cnt;
+      if (rest_cnt > 0) {
         // sort by counts
         Common::SortForPair<int, int>(counts_int, distinct_values_int, 0, true);
         // avoid first bin is zero
@@ -332,7 +335,6 @@ namespace LightGBM {
         size_t cur_cat = 0;
         categorical_2_bin_.clear();
         bin_2_categorical_.clear();
-      num_bin_ = 0;
         int used_cnt = 0;
         max_bin = std::min(static_cast<int>(distinct_values_int.size()), max_bin);
         cnt_in_bin.clear();
@@ -366,6 +368,7 @@ namespace LightGBM {
         }
         cnt_in_bin.back() += static_cast<int>(total_sample_cnt - used_cnt);
       }
+    }
 
     // check trival(num_bin_ == 1) feature
     if (num_bin_ <= 1) {
@@ -384,8 +387,12 @@ namespace LightGBM {
         CHECK(default_bin_ > 0);
       }
     }
+    if (!is_trival_) {
       // calculate sparse rate
       sparse_rate_ = static_cast<double>(cnt_in_bin[default_bin_]) / static_cast<double>(total_sample_cnt);
+    } else {
+      sparse_rate_ = 1.0f;
+    }
   }