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In general, users set the current variable (which by default is the first variable in the file) to one of those contained in the file and can then apply a number of functions and operators to them :

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setcurrent(netcdf1, 6)

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 # use the 6th variable in this netCDF file

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setcurrent(netcdf1, 2) 

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# use the 2nd variable in this netCDF file

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netcdf3 = netcdf1 op netcdf2

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out = function(netcdf1, ...)

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However, because functions and operators work only on the current variable, when the netCDF contains more than one variable (a multi-variable netcdf), special care must be taken when you need the operator/function to apply to all variables - this is detailed later in this page.

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Example 2 : To operate on two netcdf files, assigning the result to a third netcdf, you should create the output netcdf first by a simple copying of one of the input netcdfs :

# Derive cross sections of temperature forecast and analysis
# in two netcdf variables, tfc_xs and tan_xs....

(...)

# derive the list of netcdf variables
var_list = variables(tfc_xs)

# create output netcdf
diff_xs = tfc_xs

# loop over variables and create fc-an difference cross-section
for i = 1 to count(var_list) do
    setcurrent(tan_xs, i)
    setcurrent(tfc_xs, i)
    setcurrent(diff_xs, i)
    diff_xs = tfc_xs - tan_xs
end for 

Extracting NetCDF values

If you need to have access to the data values of a netcdf current variable, you can use function values() :

     val_list = values(netcdf)

which returns a vector with all the values for the current variable.You can then use the Vector functions to manipulate the data. This technique could even be used to create a new Geopoints variable with the netCDF data, or to insert the values into a GRIB field.

An alternative method for accessing individual values is to the use the function value() :

    val = value(netcdf, n)

which returns the nth value from the current netcdf variable.