Error when trying to assign values to an undefined property in an array

Question

Error when trying to assign values to an undefined property in an array

While working on a problem in Leetcode, I encountered an issue with an empty array. I attempted to push some numbers into it and received an error message that I am unsure of the reason for. Below is my code snippet:

// r and c values are pre-defined numbers, arr is also a pre-defined array.
let n = [[]]
let index = 0
for (let i = 0; i < r; i++) {
    for (let j = 0; j < c; j++) {
        n[i][j] = arr[index]
        index++;
    }
}
return n;

Leetcode flagged n[i][j] = arr[index] as erroneous.

If anyone can shed light on why this error occurred, I would greatly appreciate it. Thank you.

javascript arrays typescript

Answer 1

Answer №1

Once the variable i reaches a value of 1, it sets the value to n[i][j] within the inner loop, specifically n[1][0]. In this case, n[1] is not defined and attempting to access the 0th index of an undefined value results in an error.

The initial iteration functions correctly as there is already an empty array at the 0th index (i = 0).

To address this issue, consider utilizing the following code snippet:

let n = [];
let index = 0;
for (let i = 0; i < r; i++) {
    n[i] = [];
    for (let j = 0; j < c; j++) {
        n[i][j] = arr[index];
        index++;
    }
}

return n;

Answer 2

Once the variable i reaches a value of 1, it sets the value to n[i][j] within the inner loop, specifically n[1][0]. In this case, n[1] is not defined and attempting to access the 0th index of an undefined value results in an error.

The initial iteration functions correctly as there is already an empty array at the 0th index (i = 0).

To address this issue, consider utilizing the following code snippet:

let n = [];
let index = 0;
for (let i = 0; i < r; i++) {
    n[i] = [];
    for (let j = 0; j < c; j++) {
        n[i][j] = arr[index];
        index++;
    }
}

return n;

Answer 3

Answer №2

After receiving feedback from other users, I learned that the .push method can be used in this scenario. Here is how I incorporated that approach into my own project:

let newArray = [[]];
const rows = 6;
const columns = 9;

for (let i = 0; i < rows; i++) {
    if (i > 0) {
        newArray.push([]);
    }
    
    for (let j = 0; j < columns; j++) {
        newArray[i][j] = "y";
    }
}

console.log(newArray);

Check out my implementation on CodePen

Answer 4

After receiving feedback from other users, I learned that the .push method can be used in this scenario. Here is how I incorporated that approach into my own project:

let newArray = [[]];
const rows = 6;
const columns = 9;

for (let i = 0; i < rows; i++) {
    if (i > 0) {
        newArray.push([]);
    }
    
    for (let j = 0; j < columns; j++) {
        newArray[i][j] = "y";
    }
}

console.log(newArray);

Check out my implementation on CodePen

Error when trying to assign values to an undefined property in an array

Answer №1

Answer №2

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