How do I combine datasets from different sources or formats?

Combining datasets from different sources or formats involves three main steps: understanding data structures, cleaning/transforming data, and merging. Start by identifying each dataset’s schema, file format (CSV, JSON, SQL tables), and unique identifiers. For example, one dataset might use a timestamp in ISO format, while another uses Unix time. Aligning these requires converting data types and resolving inconsistencies. Tools like Python’s pandas or PySpark are useful for inspecting schemas programmatically. If one dataset is stored in a PostgreSQL database and another in a CSV file, you’d first extract both into a common environment (like a DataFrame) to analyze their structure.

Next, clean and transform the data to ensure compatibility. This includes handling missing values, standardizing units, and renaming columns. For instance, if one dataset lists “country” as “US” and another uses “United States,” you’ll need to map these to a consistent format. Date formats (MM/DD/YYYY vs. DD-MM-YYYY) and numerical representations (commas vs. periods for decimals) are common pain points. Use libraries like pandas for simple transformations or tools like OpenRefine for larger datasets. If merging JSON and XML data, convert both to tabular formats (e.g., CSV) or parse them into dictionaries/objects for programmatic alignment.

Finally, merge the datasets using keys or indexes. For relational data, use joins (inner, left, etc.) on shared columns like user IDs or timestamps. If datasets lack common keys, consider concatenating rows (when schemas match) or using fuzzy matching for text fields. For example, merging customer data from an API (JSON) and a legacy system (CSV) might involve joining on email addresses after ensuring both are lowercase and trimmed. Tools like pandas.merge() or SQL JOIN operations simplify this step. Always validate the merged dataset by checking row counts, null values, and sample records to ensure accuracy. Automate this workflow with scripts or pipelines (e.g., Apache Airflow) for repeatability.