3.1 Getting to know your data3.2 Variable names and labels3.3 Labeling values3.4 IDs and unique identifiers3.5 Missing values3.6 Creating new variables3.6.1 Special functions3.7 The if qualifier3.8 Changing and replacing variables3.9 Removing observations and variables3.10 Cleaning data systematically3.11 Combining datasets*3.11.1 Appending datasets3.11.2 One-to-One Merge3.11.3 Many-to-One Merge3.11.4 One-to-Many Merge3.11.5 All pairwise combinations3.12 Reshaping data*