NCL Website header
NCL Home > Documentation > Functions > Metadata routines

isatt

Returns logical values indicating whether the given attributes are attached to the given variable.

Prototype

	function isatt (
		var       ,          
		attnames  : string   
	)

	return_val [dimsizes(attnames)] :  logical

Arguments

var

A variable of any type and dimensionality.

attnames

An array of strings of any dimensionality.

Description

For each element in the attnames list, isatt returns True if the element is an attribute of var and False if not. The output of isatt is a logical array with the same dimensions as attnames. If var is not a variable, then a single missing value is returned.

This function is useful for checking if variable attributes are defined in a variable before accessing them.

See Also

iscoord, isdim, isdimnamed

Examples

Example 1

Check if a variable x has a "missing_value" attribute set. If so, use this value to set the "_FillValue" attribute, which is what NCL recognizes as the standard missing value attribute:

  if(isatt(x,"missing_value")) then
    if(.not.isatt(x,"_FillValue")) then
      x@_FillValue = x@missing_value
      delete(x@missing_value)         ; not necessary, just clean up
    else
      print("x has both a missing_value and _FillValue attribute.")
      print("The missing_value attribute will be ignored.")
    end if
  end if 

Example 2

Assume ps is a pressure variable, and we want to convert it to millibars (mb) if the units are "Pascals":

  valid_pa_units = (/"Pa","pa","PA","Pascals","pascals","PASCALS"/)

  if(isatt(ps,"units").and.any(ps@units.eq.valid_pa_units)) then
    ps = ps * 0.01
  end if