Calculated Columns

Sometimes you need a new column added automatically whose val is dependent on other fields in the same row.

Basic Example

const { Table } = require("console-table-printer");
const chalk = require("chalk");

const p = new Table({
  columns: [
    { name: "red_amount", color: "red" },
    { name: "blue_amount", color: "blue" },
  ],
  computedColumns: [
    // creating new columns based on other column vals
    {
      name: "sum",
      function: (row) => row.red_amount + row.blue_amount,
    },
    {
      name: "red_percent",
      function: (row) => {
        const val = ((row.red_amount / row.sum) * 100).toFixed(2);
        if (val <= 50) {
          return chalk.red(val);
        }
        return chalk.blue(val);
      },
    },
  ],
});

// add rows
p.addRows([
  {
    red_amount: 12,
    blue_amount: 40,
  },
  {
    red_amount: 22,
    blue_amount: 7,
  },
  {
    red_amount: 90,
    blue_amount: 10,
  },
  {
    red_amount: 1,
    blue_amount: 10,
  },
]);

// print
p.printTable();

Using All Parameters

The computed column function can take three parameters:

• row: The current row data
• index: The current row number (starting from 0)
• array: All rows in the table

Here's a simple example showing how to use each parameter:

const { Table } = require("console-table-printer");

const p = new Table({
  columns: [
    { name: "name" },
    { name: "score" }
  ],
  computedColumns: [
    // Using row: Get pass/fail status
    {
      name: "status",
      function: (row) => row.score >= 60 ? "PASS" : "FAIL"
    },
    // Using index: Add row numbers
    {
      name: "student_no",
      function: (row, index) => `Student #${index + 1}`
    },
    // Using array: Compare with class average
    {
      name: "vs_average",
      function: (row, index, array) => {
        const avg = array.reduce((sum, r) => sum + r.score, 0) / array.length;
        return row.score > avg ? "Above Average" : "Below Average";
      }
    }
  ]
});

// add rows
p.addRows([
  { name: "Alice", score: 85 },
  { name: "Bob", score: 55 },
  { name: "Charlie", score: 70 },
  { name: "David", score: 65 }
]);

// print
p.printTable();

This example shows:

1. Using row to check if a student passed
2. Using index to add student numbers
3. Using array to compare scores with class average

The output will show each student's score, their pass/fail status, student number, and how they compare to the class average.

Advanced Examples

Using Row Index for Ranking

const { Table } = require("console-table-printer");

const table = new Table({
  columns: [
    { name: "name", alignment: "left" },
    { name: "score", alignment: "right" }
  ],
  computedColumns: [
    {
      name: "rank",
      function: (row, index) => `#${index + 1}`
    },
    {
      name: "percentage",
      function: (row, index, array) => {
        const maxScore = Math.max(...array.map(r => r.score));
        return `${((row.score / maxScore) * 100).toFixed(1)}%`;
      }
    }
  ]
});

table.addRows([
  { name: "Alice", score: 85 },
  { name: "Bob", score: 92 },
  { name: "Charlie", score: 78 }
]);

table.printTable();

Complex Computations with Multiple Subjects

const { Table } = require("console-table-printer");

const table = new Table({
  columns: [
    { name: "name", alignment: "left" },
    { name: "math", alignment: "right" },
    { name: "science", alignment: "right" },
    { name: "english", alignment: "right" }
  ],
  computedColumns: [
    {
      name: "average",
      function: (row) => {
        const scores = [row.math, row.science, row.english];
        return (scores.reduce((a, b) => a + b, 0) / scores.length).toFixed(1);
      }
    },
    {
      name: "grade",
      function: (row) => {
        const avg = parseFloat(row.average);
        if (avg >= 90) return "A";
        if (avg >= 80) return "B";
        if (avg >= 70) return "C";
        if (avg >= 60) return "D";
        return "F";
      }
    },
    {
      name: "status",
      function: (row, index, array) => {
        const avg = parseFloat(row.average);
        const classAvg = array.reduce((sum, r) => sum + parseFloat(r.average), 0) / array.length;
        return avg > classAvg ? "Above Average" : "Below Average";
      }
    }
  ]
});

table.addRows([
  { name: "Alice", math: 85, science: 90, english: 88 },
  { name: "Bob", math: 92, science: 88, english: 85 },
  { name: "Charlie", math: 78, science: 82, english: 80 }
]);

table.printTable();