[{'role': 'system', 'content': "You are an expert in machine learning and your task is to classify the code snippets into categories from the provided list of categories. List of categories: ['helper_functions', 'load_data', 'data_exploration', 'data_preprocessing', 'evaluation', 'modelling', 'prediction', 'result_visualization', 'save_results', 'comment_only']"}, {'role': 'user', 'content': "Identify to which category the provided code belongs and assign the code snippet to at least 1 but up to 5 categories based on the probabilities, ignore if the probability of the category is negligible. Strictly provide your response as a list. Avoid providing any additional information, commentary, or personal opinions.\\nPython Code:import numpy as np\ndef monthly_data(df):\nmonthly_prices, periods = [], []\nperiods = []\nmy_month = df.index[0].month #checking the first month in the data\nfor j in range(df.shape[0]):\nif df.index[j].month != my_month:\nmonthly_prices.append(df['Close'][j])\nperiods.append(df.index[j])\nmy_month = df.index[j].month\nmonthly_prices = np.array(monthly_prices).astype('float32')\nreturn periods,monthly_prices"}, {'role': 'assistant', 'content': "['data_preprocessing']"}]