cdm/src/main/java/ucar/nc2/dataset/StructureDS.java
@Override
  public Structure select(List<String> memberNames) {
    StructureDS result = new StructureDS(getParentGroup(), orgVar);
    List<Variable> members = new ArrayList<>();
    for (String name : memberNames) {
      Variable m = findVariable(name);
      if (null != m) members.add(m);
    }
    result.setMemberVariables(members);
    result.isSubset = true;
    return result;
  }
@Override
  public Structure select(List<String> memberNames) {
    StructureDS result = new StructureDS(getParentGroup(), orgVar);
    List<Variable> members = new ArrayList<>();
    for (String name : memberNames) {
      Variable m = findVariable(name);
      if (null != m) members.add(m);
    }
    result.setMemberVariables(members);
    result.isSubset = true;
    return result;
  }
copy() doesnt work because convert gets called twice