aescript; arrange selected layers in a grid.

gridarrange.jsx

function gridarrange(comp, layerIndicies)
{
    var d = Math.ceil(Math.sqrt(layerIndicies.length));
    var w = comp.width / d;
    var h = comp.height / d;
    
    for (var i = 0; i < layerIndicies.length; i++)
    {
        var x = i % d;
        var y = Math.floor(i / d);
        
        comp.layers.precompose([layerIndicies[i]], comp.layers[i+1].name, true);
        
        var precomposed = comp.layers[layerIndicies[i]];
        precomposed.transform.scale.setValue([100 / d, 100 / d]);
        precomposed.transform.position.setValue([w / 2 + w * x, h / 2 + h * y]);   
    }
}

app.beginUndoGroup("gridarrange");

var item = app.project.activeItem;
var layerIndicies = [];
for (var i = 0; i < item.selectedLayers.length; i++)
{
    layerIndicies.push(item.selectedLayers[i].index);
}

gridarrange(item, layerIndicies);

app.endUndoGroup();