Alternating groups without consistent group order

[ghost]

Hi, I am looking for a way to shuffle my items based on a group membership, but I do not want each group to be spaced evenly or be in a consistent group order. My (shortened) timeline now looks like this:

timeline.push({
    // timeline
    // timeline_variables
    sample: {
        type: 'alternate-groups',
        groups: [[0,1,2,3],[4,5,6,7],[8,9,10,11],[12,13,14,15],[16,17,18,19],[20,21,22,23],[24,25,26,27],[28,29,30,31]], 
        randomize_group_order: false
    }
}

But with this sample function the group order is fixed. I want it to be completely random. Basically, I just want to ensure that members belonging to the same group are not selected right after another, but otherwise the order between the items should be completely random. Any suggestions?

[jodeleeuw]

Do you want all 32 items to be presented exactly one time? Are there any other constraints?

[ghost]

Yes, all 32 items should be presented exactly one time. There are no other constraints.

[jodeleeuw]

A custom sampling function using the shuffleNoRepeats method could work.

timeline.push({
    // timeline
    // timeline_variables
    sample: {
        type: 'custom',
        fn: function(){
		// define groups
		var groups = [[0,1,2,3],[4,5,6,7],[8,9,10,11],[12,13,14,15],[16,17,18,19],[20,21,22,23],[24,25,26,27],[28,29,30,31]];

		// create object for each timeline variable specifying group membership and item
		var all_items = [];
		for(var i=0; i<groups.length; i++){
			for(var j=0; j<groups[i].length; j++){
				all_items.push({group: i, trial_num: groups[i][j]});
			}
		}
		
		// randomize group order, with no repeat constraint
		// use custom equality function to specify what a "repeat" means
		var order = jsPsych.randomization.shuffleNoRepeats(all_items, function(a,b){
			return a.group == b.group;
		});
		
		// create the final list of trials
		return order.map(function(x){ return x.trial_num });
        }
    }
}

[becky-gilbert]

I think you meant j++ instead of i++ in the inner for loop:

for(var j=0; j<groups[i].length; j++){

[ghost]

Changing all_groups in the shuffleNoRepeats function to all_items made it work beautifully:

var order = jsPsych.randomization.shuffleNoRepeats(all_items, function(a,b){
			return a.group == b.group;
		});

Thank you both!

[jodeleeuw]

Thanks for pointing out the bugs! I've updated the code with fixes.

[suesakol]

Can I follow up on this? Would it be possible to insert attention check trials (which are of the same kind as targets) after target groups are fully randomized using the above code? Let's say I have forty target sentences. I also have three attention check trials; I'd like them to appear on trial numbers 12, 24, and 36. In that case, should I create a randomized order of the target items first and then insert attention check items into an array later?

I was thinking of something like this:

    sample: {
    type: 'custom',
    fn: function(){
	// say I have four groups and each consists of 10 items
	var groups = [ [0...9], [10.....19], [20....29], [30.....39];

	// create object for each timeline variable specifying group membership and item
	var all_items = [];
	for(var i=0; i<groups.length; i++){
		for(var j=0; j<groups[i].length; j++){
			all_items.push({group: i, trial_num: groups[i][j]});
		}
	}
	
	// randomize group order, with no repeat constraint
	// use custom equality function to specify what a "repeat" means
	var order = jsPsych.randomization.shuffleNoRepeats(all_items, function(a,b){
		return a.group == b.group;
	});
	
    
    // insert attention check trials into "order"? 
    

	// create the final list of trials
	return order.map(function(x){ return x.trial_num });
    }
}