Rust extendr/rextendr code to take R's data.frame and a file path as inputs, and save the data.frame in an Excel file

lib.rs

// Conversion of missing values doesn't work!!! -- to be corrected

use extendr_api::prelude::*;
use umya_spreadsheet::*;
use umya_spreadsheet::writer::xlsx;

#[extendr]
fn save_dataframe_to_excel(df: Robj, file_path: &str) -> extendr_api::Result<()> {
    // Ensure the input is a DataFrame
    let dataframe = df
        .as_list()
        .ok_or_else(|| extendr_api::error::Error::Other("Input is not a valid R DataFrame".to_string()))?;

    // Get column names
    let colnames = dataframe.names().ok_or_else(|| extendr_api::error::Error::Other("DataFrame has no column names".to_string()))?;

    // Create a new Excel workbook and get the active sheet
    let mut workbook = umya_spreadsheet::new_file();
    let sheet = workbook.get_active_sheet_mut();

    // Write column names to the first row of the Excel sheet
    for (col_index, colname) in colnames.into_iter().enumerate() {
        sheet.get_cell_mut((col_index as u32 + 1, 1)).set_value(colname);
    }

    // Write data to the Excel sheet
    for (col_index, (_, col)) in dataframe.into_iter().enumerate() {
        let col_data: Vec<String> = if let Some(vec) = col.as_real_vector() {
            vec.iter().map(|&v| if v.is_nan() {"NA".to_string()} else {v.to_string()}).collect() // Handle f64
        } else if let Some(vec) = col.as_integer_vector() {
            vec.iter().map(|&v| if v==-2147483648 {"NA".to_string()} else {v.to_string()}).collect() // Handle i32
        } else if let Some(vec) = col.as_str_vector() {
            vec.iter().map(|&v| v.to_string()).collect() // Handle &str
        } else if let Some(vec) = col.as_logical_vector() {
            vec.iter()
                .map(|v| {
                    if v.is_true() {
                        "TRUE".to_string()
                    } else if v.is_false() {
                        "FALSE".to_string()
                    } else {
                        "NA".to_string() // Handle NA
                    }
                })
                .collect()
        } else {
            return Err(extendr_api::error::Error::Other(
                "Unsupported column type in DataFrame".to_string(),
            ));
        };

        for (row_index, cell_value) in col_data.into_iter().enumerate() {
            sheet
                .get_cell_mut((col_index as u32 + 1, row_index as u32 + 2))
                .set_value(cell_value);
        }
    }

    // Save the workbook to the specified file path
    xlsx::write(&workbook, file_path).map_err(|e| extendr_api::error::Error::Other(format!("Failed to write Excel file: {:?}", e)))?;

    Ok(())
}
  
extendr_module! {
    mod mymodule;
    fn save_dataframe_to_excel;
}

// Note: Make sure to add `umya-spreadsheet` as a dependency in your `Cargo.toml`, like so:
// 
// [dependencies]
// extendr-api = "0.7"
// umya-spreadsheet = "2.1"