TypeScript functions for printing a matrix of data as either CSV or a markdown table

formatters.ts

type Stringable = string | { toString(): string }

export function toCSV <T extends Stringable>(items: T[][]): string {
  return items.map(row => row.join(',')).join('\n')
}

export function markdownTable (items: Stringable[][]): string {
  const asStrings = items.map(
    row => row.map(item => typeof item === 'string' ? item : item.toString())
  )

  const colSizes = asStrings.reduce<number[]>(
    (acc, line) => {
      const lineCols = line.map(col => col.length)
      return lineCols.map(
        (lineCol, index) => Math.max(lineCol, acc[index] || 0)
      )
    },
    []
  )

  const padded = asStrings.map(line =>
    line.map((col, colIndex) => {
      return ` ${col.padEnd(colSizes[colIndex], ' ')} `
    })
  )

  const asLines = padded.map(
    line => line.join('|')
  )

  const lineLen = asLines[0].length
  asLines.splice(1, 0, '-'.repeat(lineLen))

  const asTable = asLines.map(
    line => `|${line}|`
  )

  return asTable.join('\n')
}