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Scripting Guide • Programming Methods • Identifying Differences Between Strings, Lines, or Sequences
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Identifying Differences Between Strings, Lines, or Sequences
The Shortest Edit Script() function compares two strings, lines, or sequences and returns a list of changes or a matrix that describes the changes. You might use Shortest Edit Script() to identify differences between two columns, lists, or matrices. The function describes a (not the) shortest list of instructions to convert sequence A into sequence B. There might be more than one shortest script.
Example of Sequences
t1 = New Table( "t1",
New Column( "Column 1",
Numeric,
Continuous,
Format( "Best", 12 ),
Set Values( [1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 7] )
)
);
 
t2 = New Table( "t2",
New Column( "Column 1",
Numeric,
Continuous,
Format( "Best", 12 ),
Set Values( [2, 3, 4, 5, 2, 3, 4, 5, 2, 3, 4, 5, 6] )
)
);
EditScript = Shortest Edit Script( // compares column 1 in each table
sequences(
N Rows( t1 ),
N Rows( t2 ),
Function( {a, b}, // subscripts the columns
t1:column 1[a] == t2:column 1[b] // in data tables t1 and t2
)
)
);
[-1 1 . 1, // delete 1 item at position 1 in string a
0 2 1 4, // keep 4 items at position 2 in string a, position 1 in string b
-1 6 . 2, // delete 2 items at position 6 in string a
1 . 5 4, // add 4 items at position 5 in string b
0 8 9 5, // keep 5 items at position 8 in string a, position 9 in string b
-1 13 . 1] // delete 1 item at position 13 in string a
The columns in the matrix are as follows:
•
Column 1: delete the items (-1), keep the common items (0), or add the items (1)
•
Column 2: the position in string a
•
Column 3: the position in string b
•
Column 4: the number of items the instruction uses
A missing value indicates that the position isn’t used in the comparison.
Example of Separators
The following example considers “@” and “$” to be separators.
aa = "this is$a test of@shortest$edit script lines$with several words";
bb = "this is a$test of$shortest$edit script lines with several@words";
Shortest Edit Script( lines( aa, bb, separators( "@$" ) ) );
// @ and $ separators
{{"Remove", "this is$a test of@"}, {"Insert", "this is a$test of$"}, {"Common",
"shortest$"}, {"Remove", "edit script lines$with several words"}, {"Insert",
"edit script lines with several@words"}}
See “Shortest Edit Script( A, B )” in the JSL Syntax Reference for more information.