[{'role': 'system', 'content': "You are an expert in machine learning and your task is to classify code snippets into one of the following categories: ['helper_functions', 'load_data', 'data_exploration', 'data_preprocessing', 'evaluation', 'modelling', 'prediction', 'result_visualization', 'save_results', 'comment_only']."}, {'role': 'user', 'content': 'Identify the single most appropriate category to which the provided code belongs. Provide your response as a single category label without any additional information, commentary, or personal opinions.\\nPython Code:from sklearn.model_selection import train_test_split\nX_train, X_test, y_train, y_test = train_test_split( preprocessed_dataset, preprocessed_train_labels, test_size=0.2)\n\nX_train=np.expand_dims(X_train,axis=-1)\nX_test=np.expand_dims(X_test,axis=-1)\ny_train=np.array(y_train)\ny_test=np.array(y_test)\ny_train=y_train\ny_test=y_test\nprint(X_train.shape)\ny_train.max(),y_test.max()\n\n\n\n'}, {'role': 'assistant', 'content': 'data_preprocessing'}]