Hi Gregory Lypny!
One way to do this would be to change the value of both the letter and the number from the first menu. Let the first menu set the value of {letter,number} to {"A",1},{"B",1} and so on. You can define labels to each of the choices so it still shows up as "A","B" etc.
letterList = {"A", "B", "C", "D", "E", "F"};
numberList = Range[1, 10];
letterLabels =
Table[{letterList[[i]], numberList[[1]]} -> letterList[[i]], {i,
Length[letterList]}];
letter = letterList[[1]];
number = numberList[[1]];
letterLabels is what you put in the first menu, it now has the value:
{{"A", 1} -> "A", {"B", 1} -> "B", {"C", 1} -> "C", {"D", 1} ->
"D", {"E", 1} -> "E", {"F", 1} -> "F"}
This causes a problem in that when the value of {letter, number} is something like {"A",2} rather then {"A",1}, there will not exist a label to go with the value combination so the menu will display blank. This is solved using default labels, set this to be the dynamically updated value of "letter":
PopupMenu[{Dynamic[letter], Dynamic[number]}, letterLabels,
Dynamic[letter]]
PopupMenu[Dynamic[number], numberList]
Code attached, hope it helps!
Patrik
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