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Random selection without replacement

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Diane	Diane posted 11 Years Ago Topic Details Share Topic
Group: Forum Members Posts: 53, Visits: 131	Hi, I have four picture elements that randomly select an item from an item element. However, I noticed that sometimes an item is selected more than once, even though I used the "noreplace" attribute. How can I randomly select without replacement? This is the relevant part of the code: <item recallcues> </item> <trial fillrecallcues> /ontrialbegin = [item.recallcues.item=item.poweritems1.1; item.recallcues.item=item.indexitems2.1; item.recallcues.item=item.fingeritems3.1; item.recallcues.item=item.parallelitems4.1] / trialduration = 0 </trial> <picture recallcue1> /items = recallcues /select = noreplace /size = (20%,20%) / position = (10,10) </picture> <picture recallcue2> /items = recallcues /select = noreplace /size = (20%,20%) / position = (30,10) </picture> <picture recallcue3> /items = recallcues /select = noreplace /size = (20%,20%) / position = (50,10) </picture> <picture recallcue4> /items = recallcues /select = noreplace /size = (20%,20%) / position = (70,10) </picture> Thanks, Diane
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Dave	Dave posted 11 Years Ago ANSWER Post Details Share Post
Group: Administrators Posts: 13K, Visits: 108K	See e.g. https://www.millisecond.com/forums/FindPost13609.aspx. What you need to realize is that having several stimulus elements (<text>, <picture>) reference the same <item> element <picture recallcue1> /items = recallcues /select = noreplace /size = (20%,20%) / position = (10,10) </picture> <picture recallcue2> /items = recallcues /select = noreplace /size = (20%,20%) / position = (30,10) </picture> ... does not establish a single selection pool for all those stimulus elements. They are independent and each one will sample from all the items given in the <item> element without replacement. I.e. <text text1> / items = myitems / select = noreplace ... </text> <text text2> / items = myitems / select = noreplace ... </text> <item myitems> / 1 = "A" / 2 = "B" / 3 = "C" / 4 = "D" </item> is equivalent to stating <text text1> / items = ("A", "B", "C", "D") / select = noreplace ... </text> <text text2> / items = ("A", "B", "C", "D") / select = noreplace ... </text>
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Diane	Diane posted 11 Years Ago ANSWER Post Details Share Post
Group: Forum Members Posts: 53, Visits: 131	Hi Dave Thanks. That link doesnt seem to work, but perhaps my question can be solved in a different way. The reason I have made 4 recallcue picture elements is that I want four pictures at four different locations on the screen, and which picture goes where should be random. Is there a way to do that with one picture element? Thanks Diane
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Dave	Dave posted 11 Years Ago ANSWER Post Details Share Post
Group: Administrators Posts: 13K, Visits: 108K	Fixed link: https://www.millisecond.com/forums/FindPost13609.aspx And, yes, of course that's possible: <trial mytrial> / stimulusframes = [1=t1,t2,t3,t4] / validresponse = (57) </trial> <text t1> / items = myitems / position = (20%, 50%) / select = list.mylist.nextvalue </text> <text t2> / items = myitems / position = (40%, 50%) / select = list.mylist.nextvalue </text> <text t3> / items = myitems / position = (60%, 50%) / select = list.mylist.nextvalue </text> <text t4> / items = myitems / position = (80%, 50%) / select = list.mylist.nextvalue </text> <item myitems> / 1 = "A" / 2 = "B" / 3 = "C" / 4 = "D" </item> <list mylist> / items = (1,2,3,4) / selectionrate = always </list> (works the same for <picture> elements).
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