Calculating Percentage difference for a big amount of data

[#1]

Hi everyone! 
I have attached a example file under this post.
I'm currently trying to calculate the percentage of difference,
which is given by (New Value- Original Value)/Original Value
In this case, Time 0 is taken as the reference ( Original Value).
 For example:
Time: 0, Part: 1 Value 1: 690.2
Time: 50, Part:1, Value1: 690.52
(690.52-690.2)/(690.2) = 0.046%
Time: 100, Part:1, Value1:689.25
(689.25-690.2)/(690.2)= -0.13%
The result I'm suppose to get is to have a new table with the Time, id, Part unchanged,
while having the new values of Value 1 and Value 2 in percentage format. 
I have thought of moving the Different Time values into different tables,
then compute it against the Time 0 and append it to a new table, but I have no clue on 
how to write it on script. 
I have written some script in the "Percentage Different Progress" file, but I'm stuck.
I really appreciate it if anyone could help me in this. 
Thank you so so much in advance.

[#2]

If I understand what you want, I think this is the simplest way to do what you want.

dt = Current Data Table();

dt2 = dt << subset(
	Rows( dt << get rows where( Time == 0 ) ),
	columns( {"id", "Part", "Value1"} )
);

dt2:Value1 << set name( "divisor" );

dtJoin = dt << Join(
	With( dt2 ),
	Merge Same Name Columns,
	Match Flag( 0 ),
	By Matching Columns( :id = :id, :Part = :Part ),
	Drop multiples( 0, 0 ),
	Include Nonmatches( 1, 0 ),
	Preserve main table order( 1 )
);

Close( dt2, nosave );

dtJoin << New Column( "Value2",
	Numeric,
	"Continuous",
	Format( "Percent", 10, 4 ),
	Formula( (:Value1 - :divisor) / :divisor )
);

dtJoin:Value2 << delete property( "formula" );
dtJoin << delete columns( "divisor" );

[#3]

Hi Jim!
Thank you so much for the help. 
I'm wondering if there is a way 
1) to Replace the Value2 (results) in the Column Value 1 initial cells.
2) if there are actually more columns ( like 30)  that I would need to do this operation(percentage difference),
do I need to hardcode code every new column, or is there a way I could multiply or for loop the columns creation.
 

[#4 · Accepted solution]

The Value 2 results can easily replace the Value 1 results.

No you do not need to hard code the JSL for all of the columns.  I have expanded my previous code to illistrate how to run this on as many columns as there are in the data table.  I also made the assumptions that you would not want the original Value1 data changed for the Time=0 rows, but if that is not the case, then just remove the If() statement that is making that decision

Names Default To Here( 1 );
dt = Current Data Table();

// Create a subset with only the data where Time = 0
dt2 = dt << subset( Rows( dt << get rows where( :Time == 0 ) ), selected columns( 0 ) );

// Delete the Time column.  In the join step below, it
// will write on top of the original Time column if
// it remains in the subsetted data table
dt2 << delete columns( "Time" );

// Create a list of the column names so all of them can be 
// changed to a new name for the Join below.  Eliminate
// the columns "id" and "Part" from the name change since
// they will be used in the column matching in the Join.
divisorColNames = dt2 << get column names( string );
For( i = N Items( divisorColNames ), i >= 1, i--,
	If( divisorColNames[i] == "id" | divisorColNames[i] == "Part",
		divisorColNames = Remove( divisorColNames, i, 1 )
	)
);

// Rename all of the divisor columns by "adding divisor_"
// in front of each name
For( i = 1, i <= N Items( divisorColNames ), i++,
	Column( dt2, divisorColNames[i] ) << set name(
		"divisor_" || Char( Column( dt2, divisorColNames[i] ) << get name )
	)
);

// Join the data tables.  All of the matching id and part
// values will be joined to all rows with the same values
dtJoin = dt << Join(
	With( dt2 ),
	Merge Same Name Columns,
	Match Flag( 0 ),
	By Matching Columns( :id = :id, :Part = :Part ),
	Drop multiples( 0, 0 ),
	Include Nonmatches( 1, 0 ),
	Preserve main table order( 1 )
);

// The dt2 data table is no longer needed so close it
Close( dt2, nosave );

// Loop through all of the columns and create the new values
// unless the Time value is 0
For( theCol = 1, theCol <= N Items( divisorColNames ), theCol++,
	For( theRow = 1, theRow <= N Rows( dtJoin ), theRow++,
		If( dtJoin:Time[theRow] != 0,
			Column( dtJoin, divisorColNames[theCol] )[theRow] = (
			Column( dtJoin, divisorColNames[theCol] )[theRow]
			-Column( dtJoin, "divisor_" || divisorColNames[theCol] )[theRow]) /
			Column( dtJoin, "divisor_" || divisorColNames[theCol] )[theRow]
		)
	)
);

// Delete all of the no longer needed divisor columns
For( i = 1, i <= N Items( divisorColNames ), i++,
	dtJoin << delete columns( "divisor_" || divisorColNames[i] )
);

[#5]

Thank you so much Jim !