String productName = sale_obj.getString("name");

                    int quantity = Integer.parseInt(sale_obj.getString("quantity"));
                    int index = product_labels_1.indexOf(productName);
                    Log.d("products, index_before", String.valueOf(productName) + ", " + String.valueOf(quantity));

                    if (index < 0) {
                        // name doesnt exist in product_labels_1
                        Log.d("index_just_after", String.valueOf(product_labels_1.indexOf(productName)));
                        index = 0; // overwrite index
                        product_labels_1.add(quantity+" "+productName);
                        product_values_1.add(new Entry(Float.valueOf(quantity), product_labels_1.size() - 1));
                    } else {
                        // read the current quantity
                        int current_quantity = groupedProducts.getInt(productName);
                        // increment by quantity
                        quantity = current_quantity + Integer.parseInt(sale_obj.getString("quantity"));
                        Log.d("index_label_size", String.valueOf(product_labels_1.size())
                                + "//current_quantity: " + current_quantity);
                        product_values_1.set(index, new Entry(Float.valueOf(quantity), index));
                    }
                    Log.d("index_after", String.valueOf(index));
                    groupedProducts.put(productName, quantity);