Complex (for me) randomization

[David McFarlane]

Christophe,

> Ok..I finally managed to have the prog selecting one face and holding
> it for the rest of the block trials. yeepee.

You did not say how you did this, that would help us.  Just to make sure 
we are all talking about the same thing, let me lay out what I had in mind.

First, the general rule, as explained in some detail in Chapter 4 of the 
User's Guide (and I will try to word this very carefully):  The current 
value of any attribute set at one level is available to each 
successively activated lower level.

So, suppose you have a structure like

- BlockList
     - BlockProc
         - TrialList
             - TrialProc

And suppose in BlockList you have an attribute (i.e., column) named 
"Face", and that has two levels (i.e., rows) with Face set to "Bob" on 
level 1, and "Alice" for level 2.

Now, when your BlockList runs level (row) 1, all the trials in TrialList 
will use the face "Bob", and when your BlockList runs level 2 all the 
trials in TrialList will use the face "Alice".  So you see it really is 
quite simple, as you originally posed the problem.  And the rule applies 
whether you run BlockList sequentially, randomly, randomly with 
replacement, or any other way.  The key is to understand the use of 
blocks vs. trials, etc., and how attribute values propogate.

> The problem now is that
> for each new block, the prog select a face at random in the
> corresponding face list, including the face that has been presented in
> the preceding block..So I can't yet manage to have a randomized
> selection of faces without replacement through the different blocks of
> my task.

But now you add a complication.  Now you want each block to use both a 
randomly selected new face, *plus* reuse the face from the previous 
block.  Well, in general E-Prime is just not very good at remembering 
the past unless you help it along with some inline code.  The only way I 
know how to do what you now ask is to define some global variables or 
arrays and then to manage these in inline code within the program.  I 
cannot give you any more detail than that.  If you are not already a 
competent computer programmer then I advise that you now either take 
some time out to learn some real computer programming skills, or hire 
someone else for this work.

-- David McFarlane, Professional Faultfinder

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