message: Added signature only for drop_missing()
diff: @@ -100,6 +100,14 @@ enum class fill_policy : unsigned char {
  // -------------------------------------
  +enum class drop_policy : unsigned char {
  + all = 1, // Remove row if all columns are nan
  + any = 2, // Remove row if any nan column
  + threshold = 3 // Remove row if threshold number of columns are nan
  +};
  +
  +// -------------------------------------
  +
  enum class io_format : unsigned char {
  csv = 1,
  };
  @@ -348,6 +356,17 @@ public: // Other public interfaces
  const std::array<T, N> values = { },
  int limit = -1);
  + // It removes a row if any or all or some of the columns are NaN, based
  + // on drop policy
  + //
  + // types: List all the types of all data columns.
  + // A type should be specified in the list only once.
  + // threshold: If drop policy is threshold, it specifies the numbers of
  + // NaN columns before removing the row.
  + //
  + template<typename ... types>
  + void drop_missing(drop_policy policy, size_type threshold = 0);
  +
  // Make all data columns the same length as the index.
  // If any data column is shorter than the index column, it will be padded
  // by nan.
  