Determining an array index using two values

Question

Determining an array index using two values

I was struggling to find the right words for the title.

In my scenario, I have two indexes in a 2D array (x and y) that need to be multiplied together to determine the index for a second array (1D). However, it's not a straightforward calculation because if either x or y is zero, the result will always be zero no matter what the other value is.

One way to solve this problem is by using nested loops as shown below:

    int count = 0;

for( int i = 0; i < x; i++ )
{
    for( int j = 0; j < y; j++ )
    {
        count++;
    }
}

//count now has the desired value

...but this solution seems very inefficient.

It feels like this should be a simple issue to resolve, and I've been avoiding asking about it until now, hoping it would turn out to be an easy fix.

javascript arrays

Answer 1

Answer №1

To illustrate our point, let’s consider the data provided below:

let twoDimensionalArray = [[0,1,2],[3,4,5]];
let oneDimensionalArray = [0, 1, 2, 3, 4, 5];

If all subarrays possess equal lengths, one can easily determine the corresponding "row" in the 1-dimensional array by multiplying the index i with the length of each subarray and subsequently adding the "column" index.

However, this method is only applicable to matrices with fixed widths.

let subArrayLength = 3;
for (let i = 0; i < twoDimensionalArray.length; i++) {
    for (let j = 0; j < twoDimensionalArray[i].length; j++) {
        let oneDimensionalIndex = (subArrayLength * i) + j;
        console.log(twoDimensionalArray[i][j], oneDimensionalArray[oneDimensionalIndex]);
    }
}

Answer 2

To illustrate our point, let’s consider the data provided below:

let twoDimensionalArray = [[0,1,2],[3,4,5]];
let oneDimensionalArray = [0, 1, 2, 3, 4, 5];

If all subarrays possess equal lengths, one can easily determine the corresponding "row" in the 1-dimensional array by multiplying the index i with the length of each subarray and subsequently adding the "column" index.

However, this method is only applicable to matrices with fixed widths.

let subArrayLength = 3;
for (let i = 0; i < twoDimensionalArray.length; i++) {
    for (let j = 0; j < twoDimensionalArray[i].length; j++) {
        let oneDimensionalIndex = (subArrayLength * i) + j;
        console.log(twoDimensionalArray[i][j], oneDimensionalArray[oneDimensionalIndex]);
    }
}

Determining an array index using two values

Answer №1

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