Javascript :: Arrays II: NESTED ARRAYS

ArraysIi:NestedArrays1.js

// Arrays within arrays: NESTED ARRAYS / MULTIDIMENSIONAL ARRAYS
let relatedThings = [['Windows', 'MacOS'], ['New Year', 'Christmas']]
// to access 'New Year' you need to:
console.log(relatedThings[1][0]);


// using nested arrays to represent grids:
let grid = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

console.log(grid[2]); ===> [7, 8, 9]
console.log(grid[0][1]); ===> 2

// making a grid
function makeGrid(numColumns, numRows) {
  let grid = [];
  for (let i=0; i < numRows; i++) {
    let row = [];
    for (let j=1; j <= numColumns; j++) {    
      row.push(j);
    }
    grid.push(row);
  }
  console.log(grid);
  return grid;
}

// to extract a column:
let secondCol = [];
for (let i=0; i < grid.length; i++) {
    secondCol.push(grid[i][1]);
}
console.log(secondCol);

// extracts even elements into new array and puts both arrays back together
function evenAndOdd(anArr) {
  let evenArray = [];
  let newArray = [];
  let currElem = '';
  for (let i=0; i < anArr.length; i++) {
    currElem = anArr[i];
    if (currElem % 2 === 0) {
      evenArray.push(currElem);
      anArr.splice(i, 1);
    }      
  }
  newArray.push(evenArray);
  newArray.push(anArr);
  return newArray;
}

// same as above refactored
function evenAndOdd(originalArray) {
  let evenNums = [];
  let oddNums = [];
  for (let i = 0; i <= originalArray.length; i++) {
    let num = originalArray[i];
    if (num % 2) {
      oddNums.push(num);
    }
    else {
      evenNums.push(num);
    }
  }
}

// extract nested array into a flat array
function arrayFlattener(anArr) {
  let flatArr = [];
  for (let i=0; i < anArr.length; i++) {
    let element = anArr[i];
    if (Array.isArray(element)) {
      for (let j = 0; j < element.length; j++) {
        let flatElem = element[j];
        flatArr.push(flatElem);
      }
    }
    else flatArr.push(anArr[i]);
  }
  return flatArr;
}

// using .slice
function removeColumns(aGrid, numColums) {
  let slimArray = [];
  for (let i = 0; i < aGrid.length; i++) {
    let currentRow = aGrid[i];
    slimArray.push(currentRow.slice(0, currentRow.length - numColums));
  }
  return slimArray;
}

// join without using .join
function myJoin(anArray, separator = ',') {
  let joinedString = '';
  
  for (let i = 0; i < anArray.length -1; ++i) {
    const currentElem = anArray[i];
    
    if (currentElem === undefined || currentElem === null) {
      joinedString += separator;
    } else {
      joinedString += `${currentElem}${separator}`;
    }
  }
  if (anArray.length) {
  joinedString += anArray[anArray.length -1];
  }
  return joinedString;
}

// slice without using .slice
function mySlice(anArr, startIdx = 0, endIdx = anArr.length) {
  const copyArr = [];
  
  if (startIdx < 0) startIdx = anArr.length + startIdx;
  if (endIdx < 0) endIdx = anArr.length + endIdx;
  
  for (let i = startIdx; i < endIdx; ++i) {
    const currentElem = anArr[i];
    
    copyArr.push(currentElem)
  }
  return copyArr;
}