Discovering a Subarray within an Array

Question

Discovering a Subarray within an Array

I have an array called 'array'

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

and I am trying to find the index of the subarray

[1, 2, 3, 4]

However, every time I attempt this, it returns -1 instead of the expected value of 0.

This is what I have tried so far:

array.indexOf(1, 2, 3, 4);

I understand that the issue lies with the commas in the subarray I am searching for.
Can someone please advise me on how to resolve this problem?

javascript arrays indexof

Answer 1

Answer №1

One way to quickly compare arrays is by converting them into strings and then comparing those strings:

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

var target = [9, 10, 11, 12].toString();
for(var i=0; i<array.length; i++) {
   if(target === array[i].toString()) break;
}

if(i >= array.length) {
    console.log("Item not found");
} else {
    console.log("Found at position " + i);
}

Link to example

Answer 2

One way to quickly compare arrays is by converting them into strings and then comparing those strings:

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

var target = [9, 10, 11, 12].toString();
for(var i=0; i<array.length; i++) {
   if(target === array[i].toString()) break;
}

if(i >= array.length) {
    console.log("Item not found");
} else {
    console.log("Found at position " + i);
}

Link to example

Answer 3

Answer №2

One issue arises when JavaScript uses == to compare arrays and it doesn't function as expected. To solve this problem, you need to create your own array equality checker (refer to How to check if two arrays are equal with JavaScript?). Then iterate through the array and verify each sub-element to see if it matches the one you're looking for.

function arraysEqual(a, b) {
    if (a === b) return true;
    if (a == null || b == null) return false; 
    if (a.length != b.length) return false;

    // If order of elements inside array is not important, sort both arrays here.

    for (var i = 0; i < a.length; ++i) {
        if (a[i] !== b[i]) return false;
    }
    return true;
}

var haystack = [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]];
var needle = [1, 2, 3, 4];
var i = 0;

for(var sub in haystack) {
    if(array_equal(sub, needle)) { // found it
        return i;
    }
    i++;
}

if(i >= haystack.size) // didn't find it
    i = -1;

return i; // return the index of the found needle-array

Answer 4

One issue arises when JavaScript uses == to compare arrays and it doesn't function as expected. To solve this problem, you need to create your own array equality checker (refer to How to check if two arrays are equal with JavaScript?). Then iterate through the array and verify each sub-element to see if it matches the one you're looking for.

function arraysEqual(a, b) {
    if (a === b) return true;
    if (a == null || b == null) return false; 
    if (a.length != b.length) return false;

    // If order of elements inside array is not important, sort both arrays here.

    for (var i = 0; i < a.length; ++i) {
        if (a[i] !== b[i]) return false;
    }
    return true;
}

var haystack = [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]];
var needle = [1, 2, 3, 4];
var i = 0;

for(var sub in haystack) {
    if(array_equal(sub, needle)) { // found it
        return i;
    }
    i++;
}

if(i >= haystack.size) // didn't find it
    i = -1;

return i; // return the index of the found needle-array

Answer 5

Answer №3

Here's a straightforward implementation for string matching using only built-in methods and no additional variables:

[[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]
 .map( /./.test, RegExp( "^"+ [9, 10, 11, 12]+"$"  )).indexOf(true); // === 2

Answer 6

Here's a straightforward implementation for string matching using only built-in methods and no additional variables:

[[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]
 .map( /./.test, RegExp( "^"+ [9, 10, 11, 12]+"$"  )).indexOf(true); // === 2

Discovering a Subarray within an Array

Answer №1

Answer №2

Answer №3

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