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Right now I have a blank list that I am putting in Manipulate[]. I want to be able to choose whether 1,2, or 3 are in this list by setting z1,z2, z3 as True or False:

 z1 = True;
 z2 = True;
 z3 = False;
 list = {};
 For[i = 1, i <= 3, i++, 
  If[ToExpression["z" <> ToString@i], list = Insert[list, i, 1]]]

The problem comes when I put this code into Manipulate[], where I have a button called "Update list" that essentially does the process above:

 Manipulate[{list, {z1, z2, z3}}, 
  Row[{Control[{z1, {True, False}}], Control[{z2, {True, False}}], 
    Control[{z3, {True, False}}]}], 
  Button["Update list",list = {}; 
  For[i = 1, i <= 3, i++, 
 If[ToExpression["z" <> ToString@i], 
  list = Insert[list, i, 1]]]]]

But as you shall see, the button does nothing. I want:

if box "z1" is checked, 1 is added to the list. if box "z2" is checked, 2 is added to the list. ... if box "zi" is checked, i is added to the list.

How do you do this?

share|improve this question
up vote 2 down vote accepted

Your approach is so convoluted, that I find to hard to see what you are really trying to accomplish, but the following simple Manipulate accomplishes what I interpret your example code is trying to do.

Manipulate[{listy, {z1, z2, z3}},
  Row[{Control[{z1, {1, 0}}],
    Control[{z2, {1, 0}}],
    Control[{z3, {1, 0}}]}], 
  Button["Apply Filters", listy = {z1, z2, z3}],
  {{listy, {z1, z2, z3}}, None}]



Now that I understand better what you want, cosider

Manipulate[{listy, {z1, z2, z3}},
    Control[{z1, {1, 0}}],
    Control[{z2, {1, 0}}],
    Control[{z3, {1, 0}}]}], 
  Button["Apply Filters", listy = Flatten @ Position[{z1, z2, z3}, 1]],
  {{listy, {1, 2, 3}}, None}]


Perhaps you would also be interested in the more difficult case where the number of checkboxes is a parameter.

With[{n = 4},
  Manipulate[{listy, vars},
    Dynamic@Row[checkBoxes, " "],
    Button["Apply Filters", listy = Flatten@Position[vars, 1]],
    {{listy, {}}, None},
    {checkBoxes, None},
    {names, None},
    {vars, None},
    Initialization :> (
     names = Table["z" <> ToString@i, {i, n}];
     vars = ToExpression /@ names;
     checkBoxes = 
       Flatten@MapThread[{#1, Control[{#2, {1, 0}}]} &, {names,  vars}])]]


Edit 2

After some thinking, I found a way to set the number of checkboxes interactively. To do this I had to more or less turn the problem inside-out. By this I mean that, in this version, the list of checkbox values is derived from listy, rather than the other way around. I was also forced to use one of Mathematica's more obscure dynamic features to force reinitialization when the user changes the number of checkboxes. Nevertheless, the final result is a fairly compact and IMO elegant expression.

  {Sort@listy, ReplacePart[ConstantArray[0, n], List /@ listy -> 1]},
  {{n, 3, "How many checkboxes?"}, 2, 6, 1, Appearance -> "Labeled"},
  Dynamic@Row[Refresh[listy = {}, TrackedSymbols -> {n}], ""],
  {{listy, {}, ""}, Table[i -> "z" <> ToString@i, {i, n}], ControlType -> CheckboxBar}]


share|improve this answer
Hey, m_goldberg, thanks for your response. But that is not quite what I was trying to accomplish. I don't want a list of 1's. For the image you attached to your answer, I would want Apply Filters to set listy={2,3}. If all boxes are checked, I would want Apply Filters to set listy={1,2,3}. If none are checked, listy={}, and so on... Thanks a lot though for submitting a response! :) – David Aug 15 '13 at 18:22
So box z1 determines whether 1 is in the list, box z2 determines whether 2 is in the list, and so on. – David Aug 15 '13 at 18:24
I just edited the code to make it clearer what I am doing - sorry that my question was so convoluted – David Aug 15 '13 at 18:32
That works! Thanks! – David Aug 15 '13 at 20:53

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