Method MergeFrom

cpp/src/arrow/compute/kernels/aggregate_var_std.cc:149–152

Combine `m2` from two chunks (m2 = n*s2) https://www.emathzone.com/tutorials/basic-statistics/combined-variance.html

  // Combine `m2` from two chunks (m2 = n*s2)
  // https://www.emathzone.com/tutorials/basic-statistics/combined-variance.html
  void MergeFrom(const ThisType& state) {
    this->all_valid = this->all_valid && state.all_valid;
    this->moments.MergeFrom(level, state.moments);
  }

  const int level;
  const int32_t decimal_scale;