Determining if a Variable Contains a Scalar or Array Value

The SIZE function can also be used to determine whether a variable holds a scalar value or an array. Setting the DIMENSIONS keyword causes the SIZE function to return a 0 if the variable is a scalar, or the dimensions if the variable is an array, as shown in the following example:

A = 1 
B = [1] 
C = [1,2,3] 
D = [[1,2],[3,4]] 
 
PRINT, SIZE(A, /DIMENSIONS) 
PRINT, SIZE(B, /DIMENSIONS) 
PRINT, SIZE(C, /DIMENSIONS) 
PRINT, SIZE(D, /DIMENSIONS) 

IDL Prints:

0 
1 
3 
2    2