Generator of ASCII-style column graphs

asciiGraphGenerator.js

/**
 * Generates an ASCII-style (using UTF-8 characters) column graph of the provided values.
 *
 * @param {number[]} data The values to graph as columns. Each value will be represented by a single column in the graph.
 * @param {number} minY The lower bound of the Y axis.
 * @param {number} maxY The upper bound of the Y axis.
 * @param {number} scaleY The number of text rows to represent the Y axis.
 * @return {string} Generated text-based column graph.
 */
function asciiGraph(data, minY, maxY, scaleY) {
  const blocks = ['▁', '▂', '▃', '▄', '▅', '▆', '▇', '█'] // https://en.wikipedia.org/wiki/Block_Elements
  const rows = new Array(scaleY).fill('')

  for (const entry of data) {
    const adjustedValue = (Math.max(Math.min(entry, maxY), minY) - minY) / (maxY - minY) * scaleY
    const fraction = adjustedValue - Math.floor(adjustedValue)
    for (let row = 0; row < scaleY; row++) {
      if (adjustedValue > row) {
        rows[row] += blocks[blocks.length - 1]
      } else if (adjustedValue + 1 > row && fraction > 0) {
        const scaledFraction = Math.floor(fraction * blocks.length)
        rows[row] += blocks[scaledFraction]
      } else {
        rows[row] += ' '
      }
    }
  }

  return rows.reverse().join('\n')
}