Using rand(x,y) in expressions

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Using rand(x,y) in expressions

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AKrishna	AKrishna posted 6 Years Ago Topic Details Share Topic
Group: Forum Members Posts: 88, Visits: 267	Hi, just a quick question: if I set up an expression that includes a rand(x,y) function, will the random number be picked once or will it be repicked every time the expression is called? So for example: <expressions> / MyExpression = 100 + rand(-50,50) </expressions> <trial Tester> / stimulustimes = [0 = TestText] / validresponse = (" ") </trial> <text TestText> / items = ("Showing number <%expressions.MyExpression%>") </text> If trial.Tester is repeated, will there be different values for MyExpression shown? If not, are there any circumstances that might cause the expression to draw a new random number? I'm asking because the closest analogues, new elements from lists, appear to be accessed only when called via a reference to list.MyList.nextitem in an ontrialbegin/ontrialend/branch, not when referenced in a text object using <%list.MyList.nextitem%> - or at least that was my understanding. Thanks for any help!
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AKrishna	AKrishna posted 6 Years Ago ANSWER Post Details Share Post
Group: Forum Members Posts: 88, Visits: 267	+x AKrishna - Thursday, November 22, 2018 Hi, just a quick question: if I set up an expression that includes a rand(x,y) function, will the random number be picked once or will it be repicked every time the expression is called? So for example: <expressions> / MyExpression = 100 + rand(-50,50) </expressions> <trial Tester> / stimulustimes = [0 = TestText] / validresponse = (" ") </trial> <text TestText> / items = ("Showing number <%expressions.MyExpression%>") </text> If trial.Tester is repeated, will there be different values for MyExpression shown? If not, are there any circumstances that might cause the expression to draw a new random number? I'm asking because the closest analogues, new elements from lists, appear to be accessed only when called via a reference to list.MyList.nextitem in an ontrialbegin/ontrialend/branch, not when referenced in a text object using <%list.MyList.nextitem%> - or at least that was my understanding. Thanks for any help! ...and then I realized I could just run my own example code several times. So expressions do grab a new random number each time they are referenced. And it also turns out I was wrong: lists do grab new list elements even if the only reference to a new element in the trial is in a <text> stimulus using <%list.MyList.nextvalue%>. So if anyone was wondering...
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Dave	Dave posted 6 Years Ago ANSWER Post Details Share Post
Group: Administrators Posts: 12K, Visits: 98K	+x AKrishna - Thursday, November 22, 2018 +x AKrishna - Thursday, November 22, 2018 Hi, just a quick question: if I set up an expression that includes a rand(x,y) function, will the random number be picked once or will it be repicked every time the expression is called? So for example: <expressions> / MyExpression = 100 + rand(-50,50) </expressions> <trial Tester> / stimulustimes = [0 = TestText] / validresponse = (" ") </trial> <text TestText> / items = ("Showing number <%expressions.MyExpression%>") </text> If trial.Tester is repeated, will there be different values for MyExpression shown? If not, are there any circumstances that might cause the expression to draw a new random number? I'm asking because the closest analogues, new elements from lists, appear to be accessed only when called via a reference to list.MyList.nextitem in an ontrialbegin/ontrialend/branch, not when referenced in a text object using <%list.MyList.nextitem%> - or at least that was my understanding. Thanks for any help! ...and then I realized I could just run my own example code several times. So expressions do grab a new random number each time they are referenced. And it also turns out I was wrong: lists do grab new list elements even if the only reference to a new element in the trial is in a <text> stimulus using <%list.MyList.nextvalue%>. So if anyone was wondering... Just chiming in to confirm: Yes, that's correct, an expression will (and is supposed to) return a new value every time it is called. For <list> elements, things depend on their /selectionrate setting. The default behavior is /selectionrate = trial, i.e. the list will return one item from its pool when it is used in some way in a <trial>. Subsequent references to the list during that instance of the <trial> would return the same value. If the list is set to /selectionrate = always, however, it would perform a new selection every time it is referenced during a given instance of a <trial>.
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