read_csv.py

# /// script
# requires-python = ">=3.10"
# dependencies = [
#     "duckdb==1.1.1",
#     "marimo",
#     "polars==1.18.0",
#     "pyarrow==18.1.0",
#     "vega-datasets==0.9.0",
# ]
# ///

import marimo

__generated_with = "0.10.7"
app = marimo.App(width="medium")


@app.cell(hide_code=True)
def _(mo):
    mo.md(
        """
        # Read CSV

        This notebook shows how to read a CSV file from a local file or a URL into an in-memory table.
        """
    )
    return


@app.cell(hide_code=True)
def _():
    import marimo as mo
    import polars as pl

    pl.DataFrame({"A": [1, 2, 3], "B": ["a", "b", "c"]}).write_csv("data.csv")
    return mo, pl


@app.cell(hide_code=True)
def _(mo):
    mo.md("""Reading from a local CSV is as easy as `SELECT * from "data.csv"`, where `data.csv` is the path to your local file (or a URL to a CSV file).""")
    return


@app.cell(hide_code=True)
def _(mo):
    mo.accordion(
        {
            "Tip: Creating SQL Cells": mo.md(
                f"""
                Create a SQL cell in one of two ways:

                1. Click the {mo.icon("lucide:database")} `SQL` button at the **bottom of your notebook**
                2. **Right-click** the {mo.icon("lucide:circle-plus")} button to the **left of a cell**, and choose `SQL`.

                In the SQL cell, you can query dataframes in your notebook as if
                they were tables — just reference them by name.
                """
            )
        }
    )
    return


@app.cell
def _(mo):
    result = mo.sql(
        f"""
        -- Tip: you can also specify the data files using a glob, such as '/path/to/*.csv'
        -- or '/path/**/to/*.csv'
        SELECT * FROM "data.csv"
        """,
        output=False,
    )
    return (result,)


@app.cell(hide_code=True)
def _(mo):
    mo.accordion(
        {
            "Tip: Query output": mo.md(
                r"""
                The query output is returned to Python as a dataframe (Polars if you have it installed, Pandas otherwise).

                Choose the dataframe name via the **output variable** input in the bottom-left
                of the cell. If the name starts with an underscore, it won't be made available
                to other cells. In this case, we've named the output `result`.
                """
            )
        }
    )
    return


@app.cell
def _(result):
    result
    return


@app.cell(hide_code=True)
def _(mo):
    mo.md(
        r"""
        ## Create an in-memory table from a CSV file

        You can also create a table from a CSV file, so you can easily query it in subsequent cells. This table will appear in marimo's data sources panel.
        """
    )
    return


@app.cell
def _(mo):
    _df = mo.sql(
        f"""
        CREATE TABLE myTable AS SELECT * FROM "data.csv"
        """
    )
    return (myTable,)


@app.cell
def _(mo, myTable):
    _df = mo.sql(
        f"""
        SELECT * FROM myTable
        """
    )
    return


@app.cell(hide_code=True)
def _(mo):
    mo.md(r"""## Advanced usage""")
    return


@app.cell(hide_code=True)
def _(mo):
    mo.md(r"""To customize how your CSV is read, including specifying the delimiter type, use [duckdb's `read_csv` function](https://duckdb.org/docs/data/csv/overview.html).""")
    return


if __name__ == "__main__":
    app.run()