How to loop through rows from groups created by 2 columns

[#1]

Hi all,

i have a pretty simple question but unable to find the exact answer from the forum. Here's my sample data table:

Basically it has 4 columns, and i need to loop through each of combination items generating from "group 1" and "group 2", but if and only when "item" # is different then open the all  file path in "path" column. For example on first 2 rows, we have the combination is "aA", and because items also different so the script need to open both file path 1 and 2.  

[#2]

I manage to find one by create another column, "Unique":

new_col = dt << New Column("Unique", Numeric, Continuous, << Set Each Value(
	Col Sum(1, :g1, :g2); 
));



rows_to_open = dt << Get Rows Where(:ValidFile == 1 & :Unique != 1);

[#3]

You will have to modify the ValidFile calculations and possibly the row selection depending on how you build the ValidFile check.

new_col = dt << New Column("ValidFile", Numeric, Continuous, << Set Each Value(
	If(Col Sum(1, :g1, :g2, :i) == 1 & Col Number(:i, :g1, :g2) > 1,
		1
	,
		0
	);
));

[#4]

@jthi, I just want to ask a few questions with regards to the last part of the code, i.e., I don't understand it.

file_list = {};
For Each({file_path}, filepaths_to_open,
	Insert Into(file_list, Open(file_path));
);

file_list = {};

This is an empty list. The loop will fill this up via the Insert Into(file_list, Open(file_path)). Why can't one just use the list already contained in filepaths_to_open? Also, I don't understand how the Open(file_path) will insert something into the list. Isn't this just a function to open a file? How can at it all contribute to a list?

{file_path}

This, I also don't understand. Is this just a placeholder for the actual filepaths?

Maybe you have a reference explaining these things? Thank you very much already in advance.

[#5]

I think those are easiest to understand by writing a demo script ( I modified For Each a bit to add idx, it might make it a bit easier to understand how it works)

Names Default To Here(1);

filepaths_to_open = {"$SAMPLE_DATA/Big Class.jmp", "$SAMPLE_DATA/Probe.jmp", "$SAMPLE_DATA/Iris.jmp"};
show(filepaths_to_open);
file_list = {};
show(file_list);
For Each({file_path, idx}, filepaths_to_open,
	show(idx, file_path);
	Insert Into(file_list, Open(file_path));
	show(file_list);
);

• I use file_list to collect the references to the data tables which are opened (I don't need the filepaths as I already have them in the filepaths_to_open, but I don't have references)
• Open(file_path) will return a reference to the opened file and Insert Into will then add that reference to the file_list.
• The {filepath} comes from how For Each function should be used. Basically it will loop over filepaths_to_open and will return each element (one by one) in file_path variable.

filepaths_to_open = {"$SAMPLE_DATA/Big Class.jmp", "$SAMPLE_DATA/Probe.jmp", "$SAMPLE_DATA/Iris.jmp"};
file_list = {};
idx = 1;
file_path = "$SAMPLE_DATA/Big Class.jmp";
file_list = {DataTable("Big Class")};
idx = 2;
file_path = "$SAMPLE_DATA/Probe.jmp";
file_list = {DataTable("Big Class"), DataTable("Probe")};
idx = 3;
file_path = "$SAMPLE_DATA/Iris.jmp";
file_list = {DataTable("Big Class"), DataTable("Probe"), DataTable("Iris")};

Hopefully answer some of the questions.

[#6]

Yes, that was actually very useful. The file_list variable was confusing, since it is not strictly needed to open to the files (but; I take it; that it is useful later on when closing all files again (?), for example, or some other manipulation). I have to admit that it also took me some time to wrap my head around the "file_path" variable, which is assigned to a different file path at every iteration, and that it doesn't matter what it is called. (In my head, I just interpret it now as a vehicle that picks one file path after the other from the filepaths_to_open list and lets the user do "something" with it.)

Thank you! Every week a tiny growth of knowledge is better that none at all.

P.s.: The below I was only able to write based on my understanding of your explanations. Again, very useful.

Names Default To Here( 1 );

filepaths_to_open = {"$SAMPLE_DATA/Big Class.jmp", "$SAMPLE_DATA/Probe.jmp", "$SAMPLE_DATA/Iris.jmp"};

For Each( {file_path}, filepaths_to_open, Open( file_path ) );