Learn Functional Programming by Building a Spreadsheet - Step 98

JavaScript
1

Tell us what’s happening:

I tried the slice method, but it’s not working; although I tried following directions.

Your code so far

<!-- file: index.html -->
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <link rel="stylesheet" href="./styles.css" />
    <title>Functional Programming Spreadsheet</title>
  </head>
  <body>
    <div id="container">
      <div></div>
    </div>
    <script src="./script.js"></script>
  </body>
</html>

/* file: styles.css */
#container {
  display: grid;
  grid-template-columns: 50px repeat(10, 200px);
  grid-template-rows: repeat(11, 30px);
}

.label {
  background-color: lightgray;
  text-align: center;
  vertical-align: middle;
  line-height: 30px;
}

/* file: script.js */
const infixToFunction = {
  "+": (x, y) => x + y,
  "-": (x, y) => x - y,
  "*": (x, y) => x * y,
  "/": (x, y) => x / y,
}

const infixEval = (str, regex) => str.replace(regex, (_match, arg1, operator, arg2) => infixToFunction[operator](parseFloat(arg1), parseFloat(arg2)));

const highPrecedence = str => {
  const regex = /([\d.]+)([*\/])([\d.]+)/;
  const str2 = infixEval(str, regex);
  return str === str2 ? str : highPrecedence(str2);
}

const isEven = num => num % 2 === 0;
const sum = nums => nums.reduce((acc, el) => acc + el, 0);
const average = nums => sum(nums) / nums.length;

const median = nums => {
  const sorted = nums.slice().sort((a, b) => a - b);
  const length = sorted.length;
  const middle = length / 2 - 1;
  return isEven(length)
    ? average([sorted[middle], sorted[middle + 1]])
    : sorted[Math.ceil(middle)];
}


// User Editable Region

const spreadsheetFunctions = {
  sum,
  average,
  median,
  even: nums => nums.filter(isEven),
  firsttwo: nums.slice(0, 2),
  lasttwo: nums.slice(-2)
}

// User Editable Region


const applyFunction = str => {
  const noHigh = highPrecedence(str);
  const infix = /([\d.]+)([+-])([\d.]+)/;
  const str2 = infixEval(noHigh, infix);
  const functionCall = /([a-z0-9]*)\(([0-9., ]*)\)(?!.*\()/i;
  const toNumberList = args => args.split(",").map(parseFloat);
  const apply = (fn, args) => spreadsheetFunctions[fn.toLowerCase()](toNumberList(args));
  return str2.replace(functionCall, (match, fn, args) => spreadsheetFunctions.hasOwnProperty(fn.toLowerCase()) ? apply(fn, args) : match);
}

const range = (start, end) => Array(end - start + 1).fill(start).map((element, index) => element + index);
const charRange = (start, end) => range(start.charCodeAt(0), end.charCodeAt(0)).map(code => String.fromCharCode(code));

const evalFormula = (x, cells) => {
  const idToText = id => cells.find(cell => cell.id === id).value;
  const rangeRegex = /([A-J])([1-9][0-9]?):([A-J])([1-9][0-9]?)/gi;
  const rangeFromString = (num1, num2) => range(parseInt(num1), parseInt(num2));
  const elemValue = num => character => idToText(character + num);
  const addCharacters = character1 => character2 => num => charRange(character1, character2).map(elemValue(num));
  const rangeExpanded = x.replace(rangeRegex, (_match, char1, num1, char2, num2) => rangeFromString(num1, num2).map(addCharacters(char1)(char2)));
  const cellRegex = /[A-J][1-9][0-9]?/gi;
  const cellExpanded = rangeExpanded.replace(cellRegex, match => idToText(match.toUpperCase()));
  const functionExpanded = applyFunction(cellExpanded);
  return functionExpanded === x ? functionExpanded : evalFormula(functionExpanded, cells);
}

window.onload = () => {
  const container = document.getElementById("container");
  const createLabel = (name) => {
    const label = document.createElement("div");
    label.className = "label";
    label.textContent = name;
    container.appendChild(label);
  }
  const letters = charRange("A", "J");
  letters.forEach(createLabel);
  range(1, 99).forEach(number => {
    createLabel(number);
    letters.forEach(letter => {
      const input = document.createElement("input");
      input.type = "text";
      input.id = letter + number;
      input.ariaLabel = letter + number;
      input.onchange = update;
      container.appendChild(input);
    })
  })
}

const update = event => {
  const element = event.target;
  const value = element.value.replace(/\s/g, "");
  if (!value.includes(element.id) && value.startsWith('=')) {
    element.value = evalFormula(value.slice(1), Array.from(document.getElementById("container").children));
  }
}

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/125.0.0.0 Safari/537.36

Challenge Information:

Learn Functional Programming by Building a Spreadsheet - Step 98

1 Like
2

This should be a function that takes nums array as parameter, and return the first two elements of the given nums array.

Same thing as the previous line:

1 Like
3

Thanks for the confirmation. That’s what I was missing.

4

please tell me why the nums.slice has (0, 2 ) shouldn’t it be 0, 1 …and why the -2 in the lasttwo

5

an explaination would be wonderful

6

Hi there,

The syntax of the array function slice is:

Array.slice(start_index, end_index)

this will return a new array which is a portion of Array consists of elements from start_index to end_index (but element at end_index is not included).

For example:

const nums = [10, 20, 30, 40, 50, 60, 70]

nums.slice(0, 2)

will return [10, 20] because it will start from the first element (index 0) and end at the third element (index 2) but not include the third element.

nums.slice(1, 4)

will return [20, 30, 40].

One thing we need to remember is:

Array is zero-based index. Which means the first element’s index is 0, not 1.

The last element’s index is -1.
The seconde last element’s index is -2, and so on…

nums[-1] is 70
nums[-2] is 60

You can read more about Array.slice() in the document on MDN:

On a side note, if you don’t remember about any function, you can search about that function on the document.
This is a good habit for programmer as we can’t remember all the syntax.

These are my go-to sites to look up documentation:

And of course: google.

Happy coding!

4 Likes
7

thank you for your detailed explanation …i searched Google and got confused

1 Like
8

Sorry, I missed this question.

If only one argument is provide for Array.slice() instead of two arguments, then that argument is start_index.

Array.slice(start_index) will return the sub-array that start from start_index till the end of Array.

const nums = [10, 20, 30, 40, 50, 60, 70]

nums.slice(1) // return [20, 30, 40, 50, 60, 70]
nums.slice(2) // return [30, 40, 50, 60, 70]
nums.slice(-2) // return [60, 70]
2 Likes