fix

Author: Dmitry Razdoburdin

src/common/quantile.h

@@ -843,7 +843,7 @@ class SketchContainerImpl {
     dmlc::OMPException exc;
     size_t ridx_block_size = batch.Size() / n_threads_ + (batch.Size() % n_threads_ > 0);
     size_t min_ridx_block_size = 1024;
-    if ((n_features < n_threads_) && (ridx_block_size > min_ridx_block_size)) {
+    if ((n_features < size_t(n_threads_)) && (ridx_block_size > min_ridx_block_size)) {
       /* Row-wise parallelisation.
        */
       std::vector<std::set<float>> categories_buff(n_threads_ * n_features);
@@ -897,7 +897,7 @@ class SketchContainerImpl {
           size_t fidx_begin = tid * fidx_block_size;
           size_t fidx_end = std::min(fidx_begin + fidx_block_size, n_features);
           for (size_t ii = fidx_begin; ii < fidx_end; ++ii) {
-            for (size_t th = 0; th < n_threads_; ++th) {
+            for (int th = 0; th < n_threads_; ++th) {
               if (IsCat(feature_types_, ii)) {
                 categories_[ii].merge(categories_buff[th * n_features + ii]);
               } else {