[ncl-talk] A suggestion for reading variable from multiply files with different units.

[Dennis Shea]

THX for the suggestion. However, the addfiles function was developed to
allow
a heterogeneous (non-uniform) set of files to be accomodated. EG:
netCDF/GRIB/HDF
could all be accessed. The CMIP files are all CF compliant so there is some
consistency.
Other file formats (HDF) may or may not have a units attribute.

You could develop your own function [ untested ]

undef("check_units_att")
function check_units_att(f:list, varName[1]:string)
local nfils, units, nf, units_0, same_units, units_nf
begin
    nfils = ListCount(f)
   ;units= new(nfils,"string")   ; optional

    nf = 0
    if (isfilevaratt(f[nf], varName, "units")) then
        units_0   = f[nf]->$varName$@units       ; initial units
       ;units(nf) = units_0
    else
         print("check_units_att: no units attribute: "+varName+": FATAL")
         exit
    end if

    same_units = True

    do nf=1,nfils-1
         if (isfilevaratt(f[nf], varName, "units")) then
             units_nf = f[nf]->$varName$@units
            ;units(nf) = units_nf

             if (units_nf .ne. units_0) then
                ;print("units_0="+units_0+"   : units_nf="+units_nf)
                 same_units = False
             end if
       else
            print("check_units_att: no units attribute: nf="+nf)
       end if

    end do

   ;same_units at var_units = units
    return(same_units)

end



On Tue, Oct 7, 2014 at 5:47 PM, Ping Huang <ph0007 at ustc.edu> wrote:

> Dear NCL developers,
>
> I have a suggestion for reading variable from multiply files with
> different units, like xxx = infile[:]->yyy.
>
> Because of the constraint that one variable only has one unit, the unit in
> the first file is read in as the unit of input variable when reading
> multiply files.
>
> Usually, there is no problem because the multiply files from same source
> often have same unit. However, when the units in the files are different,
> for example the units of time in some CMIP5 model outputs, the input unit
> does not match with the data in other files.
>
> So, I suggest when reading multiply files the identity of all units should
> be checked. If the units are not identical, a warning should be given.
>
> Best,
>
> Ping Huang
>
>
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