Below is a script that will create the Example data table you provided. It will then create the subsets, and save each subset as a .txt file.
All that needs to be done to run this example, is to change the line of code
saveFolder = "C:\xxxxxxxxxxxxx\";
to what the actual path to the folder to save the files into, and then run the code
Names Default To Here( 1 );
// Create the example data table
New Table( "Example",
Add Rows( 7 ),
New Column( "City code", Numeric, "Continuous", Format( "Best", 12 ), Set Selected, Set Values( [32, 160, 281, 325, 420, 511, 720] ) ),
New Column( "Registration Number",
Numeric,
"Continuous",
Format( "Best", 12 ),
Set Values( [320537648, 1600084082, 2821162566, 3250488500, 4200618843, 5110680174, 7200054737] )
),
New Column( "Registration Date",
Numeric,
"Continuous",
Format( "Best", 12 ),
Set Values( [20201026, 20201020, 20201020, 20201024, 20201101, 20201027, 20200825] )
)
);
// Here is the real code.....just change the saveFolder = to the actual folder you want to
// save the files to
dt = Current Data Table();
// Create the subsets
dtSub = dt << Subset( By( :City code ),
All rows, Selected columns only( 0 ),
columns( :Registration Number, :Registration Date ) );
saveFolder = "C:\xxxxxxxxxxxxx\";
For( i = 1, i <= N Items( dtSub ), i++,
// Given the structure of the data tables created with a Subset using a By() clause
// City Code = 32
// the Word() function retuns the "32" and it is added as the name of the file to save
dtSub[i] << Save( saveFolder || Word( -1, dtSub[i] << get name, "=" ) || ".txt" )
);
Jim