Counting unique elements in a text list

Counting unique elements in a text list

The following formula will count the number of elements that are the same in a text list. 
List1 :=  @Explode ( "Red,Blue,Red,
Green,Red,Blue"; "," ) ;
List2 := List1 + "@" ;
List3 := @Unique ( List1 ) ;
List4 := @ReplaceSubstring 
( List3; List1; List2 ) ;
List5 := @ReplaceSubstring 
( List4; List3; "" ) ;
@Length ( List5 )
In this example it returns 3; 2; 1. That is, there are 3 occurrences of red, 2 blue and 1 green.

How it works

List1 can be any text list field or variable.

List2 is all the elements of List1 with @ appended to the end. You can use other characters. So, in this example, List2 looks like: 

 Red@; Blue@; Red@; Green@; Red@; Blue@
List3 is a text list of the unique values within List1: 
 Red; Blue; Green
List4 replaces the values in List3 with those in List2, which results in an @ sign for each occurrence: 
 Red@@@; Blue@@; Green@
List5 removes the List3 values from List4 and returns: 
 @@@; @@; @
The last command now returns the length of each item in the list: 
 3; 2; 1
With a bit more list manipulation you can return:

Red 3
Blue 2
Green 1

List1 :=  @Explode ( "Red,Blue,Red,
Green,Red,Blue"; "," ) ;
List2 := List1 + "@" ;
List3 := @Unique ( List1 ) ;
List4 := @ReplaceSubstring ( List3;
 List1; List2 ) ;
List5 := @ReplaceSubstring ( List4; 
List3; "" ) ;
@Length ( List5 )

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This was first published in November 2003

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