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venn2_intersection

Returns the unique element intersection (ie., common values) between two arrays.

Available in version 6.4.0 and later.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"  ; This library is automatically loaded
                                                             ; from NCL V6.2.0 onward.
                                                             ; No need for user to explicitly load.

	function venn2_intersection (
		a  : numeric, string, character,  
		b  : numeric, string, character   
	)

	return_val [*] :  same type as a

Arguments

An array of any shape and size.

An array of the same type as a. It may have a different size and shape.

Return value

A scalar or one-dimensional array containing the elements that form the intersection of the input arrays. The result is independent of the input order.

Description

The INTERSECTION of two sets (here, a and b) is the set of elements which are in both sets. For example: let A = (1,2,3) and B = (3,4,5). The INTERSECTION of A and B, written A intersection B = (3).

NCL has a limited suite of simple Venn_diagram functions: (i) venn2_difference, (ii) venn2_intersection and (iii) venn2_union. Pictoral depictions are here.

Examples

Example 1

Return the intersection of two arrays. Note that the result is independent of the input order.

  A   = (/"a", "e", "i", "o", "u", "y" /)
  B   = (/"a", "b", "c", "d", "e", "f", "g", "h" /)

  ABi = venn2_intersection(A, B)    ; ABi = (/"a", "e"/)
  BAi = venn2_intersection(B, A)    ; BAi = (/"a", "e"/)

Example 2: Return the unique intersection elements of three arrays. The result is independent of the input order.

  A   = (/"a", "e", "i", "o", "u", "y" /)
  B   = (/"a", "b", "c", "d", "e", "f", "g", "h" /)
  C   = (/"a","b", "q", "y", "z"/)

  AC  = array_append_record(A, C, 0) ; AC = (/"a","e","i","o","u","y","a", "b", "q", "y", "z"/)

  ACBi = venn2_intersection(AC,B)  ; ACBi= (/"a","b","e" /)

Example 3

  date1 = (/"1979-01-01-00000","1979-01-02-00000","1979-01-08-00000","1979-01-06-00000" \
           ,"1980-12-12-00000","1981-01-02-00000","1988-05-06-00000","1988-05-06-00000" /)

  date2 = (/"1979-05-01-00000","1979-01-01-00000","1979-01-06-00000","1981-01-02-00000" \
           ,"1981-01-02-00000","1987-01-02-00000","1988-05-06-00000"/)

  DATE  = venn2_intersection(date1, date2) 
  print(DATE)

The output would be


   Variable: DATE
   Type: string
   Total Size: 32 bytes
               4 values
   Number of Dimensions: 1
   Dimensions and sizes:   [4]
   Coordinates: 
   Number Of Attributes: 2
     _FillValue :  missing
     tag : NCL: venn2_intersection has created the result
   (0)     1979-01-01-00000
   (1)     1979-01-06-00000
   (2)     1981-01-02-00000
   (3)     1988-05-06-00000

Example 4: The venn2_intersection allows arrays of different sizes and shapes.

  y   = (/ (/1.5, 2.8, 1.6/), (/3.1, 1.5,-9.9/), (/2.8, 2.8, 2.8/) /)   ; 3 x 3 
  x   = (/   1.5, 1.6, 3.1, 2.8, 2.8 /)   ; [5]   
  yxi = venn2_intersection(y3, x)    ; yxi = (/1.5, 1.6, 2.8, 3.1/)

Example 5: Use all three Venn based venn2_* functions.