pro SUB_accumulate_step5_singlelevel, var_combine, var_mean_all, var_std_all, var_mean, var_std

  if n_elements(var_mean_all) eq 0 then begin ; the first element, simply give the current value

    var_mean_all =  reform(var_mean, [1, size(var_mean, /dim)])
    var_std_all  =  reform(var_std,  [1, size(var_std, /dim)])

  endif else begin

        var_mean_all = [var_mean_all, ]
        var_std_all[-1, this_id] = var_std[combine_loop]

        if ARG_PRESENT(nobs_this) then begin
          var_nobs_all[-1, this_id] = nobs_this[combine_loop]
        endif

    endfor ; combine_loop

  endelse  ; n_elements(var_mean_all) eq 0 

end