Support excel export in some way

[aszenz]

Currently it's difficult to export data from perspective to excel since excel by default cannot guess separators in the csv, it uses a fixed separator based on the region/language which doesn't work for non-US installations.

For many people excel is the only tool to open csv's.

This can be solved by either a dedicated excel export or a csv format that excel can open easily in different regions/languages.

[aszenz]

I added excel export myself using https://github.com/estie-inc/wasm-xlsxwriter

Here's a basic version that creates an excel table out of a perspective view, rendering it in the worksheet (without support for grouped cols)

import type { View } from "@finos/perspective";
import xlsxInit, { Workbook, Table, TableColumn } from "wasm-xlsxwriter/web";

async function toExcel(view: View, sheetName: string) {
  await xlsxInit();
  const workbook = new Workbook();
  const worksheet = workbook.addWorksheet();
  worksheet.setName(sheetName);
  const table = new Table();
  const data = (await view.to_columns()) as Record<string, Array<unknown>>;
  const columns: TableColumn[] = [];
  const dataRowIndexStart = 2; // 3rd row;
  const dataColIndexStart = 1; // 2nd col;
  Object.entries(data).forEach(([columnName, value], index) => {
    const tblCol = new TableColumn().setHeader(columnName);
    columns.push(tblCol);
    worksheet.writeColumn(
      dataRowIndexStart,
      index + dataColIndexStart,
      // TODO: Handle other types
      value,
    );
  });
  const rows = await view.num_rows();
  const cols = await view.num_columns();
  const tbl = table.setName(sheetName).setColumns(columns);
  worksheet.addTable(
    dataRowIndexStart - 1,
    dataColIndexStart,
    dataRowIndexStart + rows - 1,
    dataColIndexStart + cols - 1,
    tbl,
  );
  return workbook.saveToBufferSync();
}