This post will be short, I recently built a WASM app that allows you to 1) convert between Parquet/CSV/JSON and 2) explore the data using Marimos built-in tooling.

I shared an initial introduction to marimo in a blog earlier.

Tip

In short marimo is an up-and-coming Notebook that also have “App-mode” and can run using WASM.

App:Converter

There’s multiple libraries suppoted in Pyodide, Python WASM, among them: polars, duckdb and pandas.
All these libraries are exceptional, with pandas as a exception 😉, to do Data Science and work with tabular data. They also have read/write support for JSON, CSV and parquet files.

Tip

Parquet is an awesome format for reading data, it’s small, fast & efficient which in turn enables magnitudes better performance (10-100x easily).

These tools enable my simple converter that allows more people to easily move from CSV/JSON to Parquet, and in turn have faster plotting!

As always there’s some problems implementing:

polars doesn’t support parquet/JSON in WASM
- –> fall-back to duckdb.
- duckdb can’t read parquet fromio.BytesIO
  - –> fall-back to… pandas 🤦‍♂️.
  - Luckily we can quickly call pl.from_pandas to run polars!

I hope to add more formats moving forwards, such as ndjson and xlsx.

Convert (src: parquet-file) that automatically infer available targets

App:Explore

Data Exploration - a important part and initial step when working with data of any type.
When exploring your dataset it’s good to have a streamlined way of working. Marimo has some excellent tooling to quickly structure your data. I’ve added all these tools in my simple WASM app, things include like:

**DataFrame with Statistics in the header**

These tools combine into a quite neat exploration app. If you run this notebook locally you can easily hit up the code cells and modify the DataFrames manually and keep utilizing the nifty UI features such as statistics in DataFrame columns or visualization.

All in all this is a simple quick-starter, I think this app can be helpful for those who wants to explore their data, advaned or simple.

Result

WASM Spreadsheet Explorer/Converter (CSV, JSON & Parquet) App

Also available as stand-alone

Outro

I’ll keep adding more WASM apps with time. I love Pyodide.

Combining WASM with Marimo, or stlite, feels like such a natural fit.
Marimo to me combines the perfection of Notebook Exploration with Apps, hence I opted for Marimo now.

Moving on I’ll add more in-depth blogs about Marimo and why it’s awesome, embedding WASM snippets and more.

Thanks for this time,
Hampus Londögård