4.1.6 Attributes

Attributes are referred to by var_nm@att_nm
All the following are valid statements:

     global@text="Test Attributes"; /* Assign a global variable attribute */
     a1[$time]=time*20;
     a1@long_name="Kelvin";
     a1@min=a1.min();
     a1@max=a1.max();
     a1@min++;
     --a1@max; q
     a1(0)=a1@min;
     a1($time.size-1)=a1@max;

A value list can be used on the RHS of an assign...

     a1@trip1={1,2,3} ;
     a1@triplet={a1@min,(a1@min+a1@max)/2,a1@max};

The netCDF specification allows all attribute types to have a size greater than one. The maximum is defined by NC_MAX_ATTRS. The following is an ncdump of the metadata for variable a1

     double a1(time) ;
       a1:long_name = "Kelvin" ;
       a1:max = 199. ;
       a1:min = 21. ;
       a1:trip1 = 1, 2, 3 ;
       a1:triplet = 21., 110., 199. ;

The size() method can be used with attributes. For example, to save an attribute text string in a variable,

     defdim("sng_len", a1@long_name.size());
     sng_arr[$sng_len]=a1@long_name; // sng_arr now contains "Kelvin"

Attributes defined in a script are stored in memory and are written to Output after script completion. To stop the attribute being written use the ram_delete() method or use a bogus variable name.

Attribute Propagation & Inheritance

• Attribute propagation occurs in a regular assign statement. The variable being defined on the LHS gets copies of the attributes from the leftermost variable on the RHS
• Attribute Inheritance: The LHS variable "inherits" attributes from an Input variable with the same name
• It is possible to have a regular assign statement for which both propagation and inheritance occur.

     prs_mdp[time,lat,lon,lev]=P0*hyam+hybm*PS;   // prs_mdp gets attributes from PO
     th_min=1.0 + 2*three_dmn_var_dbl.min($time); // th_min  gets attributes from three_dmn_var_dbl

If the attribute name contains non-regular characters use ID quoting. See see ID Quoting

     'b..m1@c--lost'=23;