Data Engineering Engineering

Flattening Nested JSON to Tabular CSV for Analytics

Learn how to flatten multi-level JSON arrays into tabular CSV files with dot-notation headers for Excel, Google Sheets, and Pandas.

Business analysts, data scientists, and finance teams require rectangular spreadsheets for Excel and BI dashboards. However, modern REST APIs return deeply nested JSON objects. This guide explains the recursive flattening algorithms used to translate nested trees into clean tabular CSV columns.

Dot-Notation Column Normalization

When an object contains nested child objects, the flattening algorithm flattens keys hierarchically using dot-notation (e.g. user.address.postalCode).

json
[
  {
    "orderId": "ORD_9901",
    "customer": { "name": "Elena", "email": "[email protected]" },
    "total": 149.99
  }
]

Translates into the tabular CSV representation:

csv
orderId,customer.name,customer.email,total
ORD_9901,Elena,[email protected],149.99

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Frequently Asked Questions

How are nested arrays handled in CSV export?

Nested arrays can either be serialized as JSON strings inside the cell or joined as semicolon-separated lists.

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