Random Sampling of Zotero Items

/*
 Based on batch editing script from zuphilip
 
 How does this work?
 0) make a backup copy
 1) create a collection of all entries you want to randomly sample
 (maybe use a smart search or drag and drop, delete individual items)
 2) check that you have exactly the items you want to change in your collection
 3) choose one example here and adapt it to your needs
 4) run the code
 5) save the log if needed
*/

// Example 1: set a fixed value in a field
// (the field must be a simple field)
var action = 'set';
var field = 'callNumber'; // puts the sample index in the Call Number field
var weights = [0.96, 0.04]; // enter the probablity of being not-sampled and sampled (sum to 1)
var results = [0, 1]; // values for not-sampled and sampled

function getRandom () {
    var num = Math.random(),
        s = 0,
        lastIndex = weights.length - 1;

    for (var i = 0; i < lastIndex; ++i) {
        s += weights[i];
        if (num < s) {
            return results[i];
        }
    }

    return results[lastIndex];
};

var items = [];
var fieldID = Zotero.ItemFields.getID(field);
var selectedCollection = ZoteroPane.getSelectedCollection();
var selectedSavedSearch = ZoteroPane.getSelectedSavedSearch();

if (!selectedCollection && !selectedSavedSearch) {
  alert('Select a Collection or Saved Search first');
}

if (selectedCollection) {
  items = selectedCollection.getChildItems();
  if (!confirm('Do you want to change these ' + items.length + ' items in collection ' + selectedCollection.name + '?')) {
    items = [];
  }
}

if (selectedSavedSearch) {
  var ids = selectedSavedSearch.search();
  for (var k=0; k<ids.length; k++) {
  items[k] = Zotero.Items.get(ids[k]);
  }
  if (!confirm('Do you want to change these ' + items.length + ' items in collection ' + selectedSavedSearch.name + '?')) {
    items = [];
  }
}

for (var i=0; i<items.length; i++) {
  //set single fields
  if ( fieldID && Zotero.ItemFields.isValidForType(fieldID, items[i].itemTypeID) ) {
  var content = items[i].getField(field);
  var updatedValue = getRandom();
  console.log(items[i].itemID + ' : ' + field + ' : ' + content + ' -> ' + updatedValue);
  items[i].setField(field, updatedValue);
  items[i].save();
  continue;
  }
  console.log(items[i].itemID + ' : type ' + items[i].itemTypeID + ' : field ' + field + ' untouched' );
}