GrADS Function: if

if()

This function performs an if/then/else expression evaluation. It is available starting with GrADS version 2.1.1.b0.

Syntax

if (logical_expr, then_expr, else_expr)

where:

logical_expr   - any valid logical expression that has a boolean (yes/no) result
then_expr      - the result expression if logical_expr is true
else_expr      - the result expression if logical_expr is false

All the arguments must be expressions for gridded data -- the logical operators and the if() function have not yet been implemented for station data.

Usage Notes

The logical_expr should include one or more of the logical operators: =, !=, >, >=, <, <=, |, &

The result of a logical operation is boolean -- an answer to a yes/no question. If the expression is true the result is 1, and if the expression is false the answer is -1. The if() function will evaluate logical_expr and wherever the result is >0 it will place the value of then_expr, and wherever the result is <0 it will place the value of else_expr.
The argumentsthen_expr and else_expr may be any GrADS expression, including a constant. If you want then_expr or else_expr to be undefined, then use maskout() instead of the if() function.

Examples

Here is a script sample to find the minimum and maximum 2-meter temperature at each grid point over a 12-month period:


  'define tmin = const(t2m,1e9)'

  'define tmax = const(t2m,-1e9)'

  t = 1

  while (t <= 12) 

  'set t 't

  'define tmin = if(t2m<tmin,t2m,tmin)'

  'define tmax = if(t2m>tmax,t2m,tmax)'

  t = t + 1

endwhile