Unrolling a matrix array - TypeError: Cannot read property 'reverse' of undefined

user_16198542 0
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I'm trying to practice solving JS coding problems. Given an array matrix, unroll the array in clockwise rotation.

// Sample Array 
//  1  2  3  4
//  12 13 14 5
//  11 16 15 6
//  10 9  8  7  

matrix = [[1, 2, 3, 4], [12, 13, 14, 5], [11, 16, 15, 6], [10, 9, 8, 7]]  

// expected output
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]  


matrix2 = [["a", "b", "c"], ["d", "e", "f"], ["g", "h", "i"]]  

// expected output  
["a", "b", "c", "f", "i", "h", "g", "d", "e"]

I wrote the following solution, but it keeps crashing when it tries to revere the bottom array. I keep getting Uncaught TypeError: Cannot read property 'reverse' of undefined.

What is odd about this is that I found multiple solutions online to this coding challenge, and they're all similar to this solution. I tried copying/pasting these solutions, but when I run them, I still get the same error above. (example 1, example 2).

How can I improve my code to avoid this error and achieve the desired results?

function unrollMatrix(array) {

    let newArray = [];

    while (array.length > 0) {

        // Get top row 
        results = [...newArray, array.shift()];

        // Get right column
        results = [...newArray, array.map(row => row.pop())];

        // Get bottom row in reverse 
        results = [...newArray, array.pop().reverse()];

        // Get left column in reverse 
        results = [...newArray, array.map(row => row.shift()).reverse()];
    }

    return newArray.flat();
}
data-structures arrays javascript
1 Answers

You have not assigned any value to newArray. Rest of the code looks fine, just assign values to newArray instead of result.

let matrix = [
  [1, 2, 3, 4],
  [12, 13, 14, 5],
  [11, 16, 15, 6],
  [10, 9, 8, 7]
];

function unrollMatrix(array) {

  let newArray = [];

  while (array.length > 0) {

    // Get top row 
    newArray = [...newArray, array.shift()];

    // Get right column
    newArray = [...newArray, array.map(row => row.pop())];

    // Get bottom row in reverse 
    newArray = [...newArray, array.pop().reverse()];

    // Get left column in reverse 
    newArray = [...newArray, array.map(row => row.shift()).reverse()];
  }
  return newArray.flat(1);
}

let ans = unrollMatrix(matrix);

console.log(ans);

user_67907440
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