[{'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:def calculatePerKeyDwellTime(dataframe):\ndwell_times = {}\nfor i in set(dataframe.key.unique()):\nrunning_average = 0;\nsubset = dataframe[dataframe['key'] == i];\nif(len(dataframe[dataframe['key']==i])%2==0):\nfor g in range(len(subset)-1):\nrunning_average+=(float(subset.iloc[g+1]['timestamp']) - float(subset.iloc[g]['timestamp']));\nrunning_average/=len(subset);\nelse: # last key release not recorded\nfor g in range(len(subset)-2):\nrunning_average+=(float(subset.iloc[g+1]['timestamp']) - float(subset.iloc[g]['timestamp']));\nrunning_average/=len(subset);\ndwell_times[i] = running_average;\nreturn dwell_times;"}, {'role': 'assistant', 'content': "['data_preprocessing']"}]