compute two greatest numbers in 3 styles.

example-1-self-documenting-code.js

function computeTwoGreatestNumbersFromListOfNumbers(listOfNumbers) {
  return listOfNumbers.reduce(
    (currentlyKnownGreatestValues, currentValueWhileIterating) => {
      if (currentValueWhileIterating > currentlyKnownGreatestValues[0]) {
        return [currentValueWhileIterating, currentlyKnownGreatestValues[0]];
      } else if (currentValueWhileIterating > currentlyKnownGreatestValues[1]) {
        return [currentlyKnownGreatestValues[0], currentValueWhileIterating];
      } else {
        return currentlyKnownGreatestValues;
      }
    },
    [Number.NEGATIVE_INFINITY, Number.NEGATIVE_INFINITY]
  );
}

let testActualVsExpected = (a, e) =>
  console.log(a[0] === e[0] && a[1] === e[1] ? "pass" : "fail");

let typicalExample = [2, 7, 5, 9];
testActualVsExpected(
  computeTwoGreatestNumbersFromListOfNumbers(typicalExample),
  [9, 7]
);

let duplicateValuesExample = [2, 9, 9, 7];
testActualVsExpected(
  computeTwoGreatestNumbersFromListOfNumbers(duplicateValuesExample),
  [9, 9]
);

let ascendingOrderExample = [1, 2, 3, 4];
testActualVsExpected(
  computeTwoGreatestNumbersFromListOfNumbers(ascendingOrderExample),
  [4, 3]
);

let descendingOrderExample = [9, 6, 5, 2];
testActualVsExpected(
  computeTwoGreatestNumbersFromListOfNumbers(descendingOrderExample),
  [9, 6]
);

example-2-literate-with-comments.js

// # Compute the largest and second largest values from a list of numbers.
//
// This code example is written in a literate programming style 
// and intentionally uses terse names.
//
// let m be the smallest possible number.
// let c be a function that computes the two greatest numbers.
// let l be the list of numbers.
// let p be the two greatest known values while iterating over the list, defaulted to [m, m].
// let v be the current number while iterating over the list. 

// Handle three cases:
// If v is greater than 1st value in p then set p to [v, p[0]]. 
// ElseIf v is greater than 2nd value in p then set p to [p[0], v]. 
// Otherwise v is smaller than both values in p, p remains unchanged.

const m = Number.NEGATIVE_INFINITY;

const c = l =>
  l.reduce(
    (p, v) => (v > p[0] ? [v, p[0]] : v > p[1] ? [p[0], v] : p),
    [m, m]
  );


// ## Test 4 cases to verify correctness. 
// 
// let t be a function to compare actual and expected and return "pass" or "fail".
// let a be the actual result.
// let e be the expected result.
let t = (a, e) => console.log(a[0] === e[0] && a[1] === e[1] ? "pass" : "fail") 

// Test typical case.
t( c([2,7,5,9]), [9,7] )

// Test duplicates case.
t( c([2,9,9,7]), [9,9] ) 

// Test ascending list case.
t( c([1,2,3,4]), [4,3] ) 

// Test descending list case.
t( c([9,6,5,2]), [9,6] )

example-3-true-literate-style.md

Compute the largest and second largest values from a list of numbers.

This code example is written in a literate programming style and intentionally uses terse names.

let m be the smallest possible number. let c be a function that computes the two greatest numbers. let l be the list of numbers. let p be the two greatest known values while iterating over the list, defaulted to [m, m]. let v be the current number while iterating over the list.

Handle three cases: If v is greater than 1st value in p then set p to [v, p[0]]. ElseIf v is greater than 2nd value in p then set p to [p[0], v]. Otherwise v is smaller than both values in p, p remains unchanged.

const m = Number.NEGATIVE_INFINITY;

const c = l =>
  l.reduce(
    (p, v) => (v > p[0] ? [v, p[0]] : v > p[1] ? [p[0], v] : p),
    [m, m]
  );

Test 4 cases to verify correctness.

let t be a function to compare actual and expected and return "pass" or "fail". let a be the actual result. let e be the expected result.

let t = (a, e) => console.log(a[0] === e[0] && a[1] === e[1] ? "pass" : "fail") 

Test typical case.

t( c([2,7,5,9]), [9,7] )

Test duplicates case.

t( c([2,9,9,7]), [9,9] ) 

Test ascending list case.

t( c([1,2,3,4]), [4,3] ) 

Test descending list case.

t( c([9,6,5,2]), [9,6] )