subscripting list with 2d matrix

vince_faller

I would really love it if we could subscript a list with a matrix and have it shape the list into a list of lists.  

 

 

l = {"A", "B", "C", "D", "E", "F"};
ss = [1 2, 3 4, 5 6];

l[ss]; // I want this to come out as {{"A", "B"}, {"C", "D"}, {"E", "F"}};

 

 

 

 

gzmorgan0

@vince_faller ,

I have a slightly more generic wish. But decided to pile on.  It is a repeat wish for a function that evaluates each item in a list, much like a function is appleid to each element in a matrix.

 

If available, then 

l[ AsList( ss ) ] would return the desired result.

 

I use LFunc() often.  I wish it were a built in capability. A script is attached with my version of a function. Remove /* at line 81 to  

 

l = {"A", "B", "C", "D", "E", "F"};
ss = [1 2, 1 4, 5 2];
ssl = As List(ss);

rst = Lfunc(ssl,Expr(l[x]));
show(l, ssl,rst);

Log output

/*:

ssl = {{1, 2}, {1, 4}, {5, 2}};
rst = {{"A", "B"}, {"A", "D"}, {"E", "B"}};

In case someone on the blog might be interested.

 

Lfunc = Function( {xList, fExpr/*ex. Expr(Contains(x,"h"))*/},
	{x = {}, i = 1, errCode = 0, errStr = "\!NError bad argument", newExpr},
	If( !Is List( xList ),
		errCode = 1
	);
	If(
		Type( Name Expr( fExpr ) ) == "Name", 
 //if Name then JMP does not recognize the function
			tmp = Trim( Char( Name Expr( fExpr ) ) );
  //extract the function and check if it is contained in the global namespace, if not error!
			If( Namespace( "global" ) << Contains( Word( 1, tmp, ":(" ) ) == 0,
				errCode = errCode + 2
			);,
		Type( Name Expr( fExpr ) ) != "Expression", errCode = errCode + 2
	); 
 //catches typos, returns Name if not a valid function
	//catches typos, returns Name if not a valid function
	If( !Is Expr( Name Expr( fExpr ) ),
		errCode = errCode + 2
	);   //catches syntax
	If(
		!errCode,
			For( i = 1, i <= N Items( xList ), i++,
				newExpr = Substitute( Name Expr( fExpr ), Expr( x ), xList[i] );
				insert Into(x, "");
				x[i] = Eval(Expr(Try( newExpr, Empty() )));
			),
		errCode == 1, Write( errStr || "(1) not a list \!N" ),
		errCode == 2, Write( errStr || "(2) not a valid expression \!N" ),
		errCode == 3, Write( errStr || "s (1) is not a list and (2) is not a valid expression \!N" )
	);
	x//return x
	;
); //End Lfunc




l = {"A", "B", "C", "D", "E", "F"};
ss = [1 2, 1 4, 5 2];
ssl = As List(ss);

rst = Lfunc(ssl,Expr(l[x]));
show(l, ssl,rst);

Lfunc = Function( {xList, fExpr/*ex. Expr(Contains(x,"h"))*/},
	{x = {}, i = 1, errCode = 0, errStr = "\!NError bad argument", newExpr},
	If( !Is List( xList ),
		errCode = 1
	);
	If(
		Type( Name Expr( fExpr ) ) == "Name", 
 //if Name then JMP does not recognize the function
			tmp = Trim( Char( Name Expr( fExpr ) ) );
  //extract the function and check if it is contained in the global namespace, if not error!
			If( Namespace( "global" ) << Contains( Word( 1, tmp, ":(" ) ) == 0,
				errCode = errCode + 2
			);,
		Type( Name Expr( fExpr ) ) != "Expression", errCode = errCode + 2
	); 
 //catches typos, returns Name if not a valid function
	//catches typos, returns Name if not a valid function
	If( !Is Expr( Name Expr( fExpr ) ),
		errCode = errCode + 2
	);   //catches syntax
	If(
		!errCode,
			For( i = 1, i <= N Items( xList ), i++,
				newExpr = Substitute( Name Expr( fExpr ), Expr( x ), xList[i] );
				insert Into(x, "");
				x[i] = Eval(Expr(Try( newExpr, Empty() )));
			),
		errCode == 1, Write( errStr || "(1) not a list \!N" ),
		errCode == 2, Write( errStr || "(2) not a valid expression \!N" ),
		errCode == 3, Write( errStr || "s (1) is not a list and (2) is not a valid expression \!N" )
	);
	x//return x
	;
); //End Lfunc

/*

//Usage & Test ...remove the slash asterisk and run in segments, results are in the log
//------------------------------------------------------------------------------    
  myList={"john", "harry", "huh","ah ha", "xyx", , "a", "h", 7, [1,7]};
  
  /* returns a list of numeric values, one value for each item in the list 
//   n =>1st location of h, 0 => does not contain, Empty() => the item is not 
//   a valid argument for that expression.
//  */
zz = Lfunc(myList,Expr(Contains(x,"h")));  
myList={"john", "harry", "huh","ah ha", "xyx", , "a", "h"};
zz=Lfunc(myList, Expr(Uppercase(x)));
show(zz);
-----------------------------------------------------------------------------------------
/* returns a list of how many words are in each string 
   [] -> no occurrences
   Empty() => the expression is not valid for that item.
*/

zz = Lfunc(mylist, expr(nitems(words(x))));
show(zz);
-----------------------------------------------------------------------------------------
/* This specified function requires numeric arguments 
   Empty() => the expression is not valid for that item.
   A numeric function applied to a matrix returns a matrix 
   of the results applied on each element in the matrix.
   Only the last 2 items are valid arguments for Log()
*/
  myList={"john", "harry", "huh","ah ha", "xyx", , "a", "h", 7, [1,7]};

zz = Lfunc(mylist, expr(log(x)));
show(zz);
----------------Error Checking---------------------------------------------------------------
zz = Lfunc("oh johhny", Expr(Contains(x,"h")) );     //not a list
show(zz);
zz = Lfunc({"oh johhny"}, Expr(Contians(x,"h")) );  //type not a valid expr due to typo
show(zz);
zz =  Lfunc("oh johhny", Expr(Contians(x,"h")) );   //not a list and not a valid expr
show(zz);
----- end test */