code: @NotNull
      public static <T> Collector<T, ?, Double> averagingInt(@NotNull final ToIntFunction<? super T> mapper) {
          return averagingHelper(new BiConsumer<long[], T>() {
              @Override
              public void accept(long[] t, T u) {
                  t[0]++; // count
                  t[1] += mapper.applyAsInt(u); // sum
              }
          });
      }
docs: Returns a {@code Collector} that calculates average of integer-valued input elements.
  
  @param <T> the type of the input elements
  @param mapper  the mapping function which extracts value from element to calculate result
  @return a {@code Collector}
  @since 1.1.3