I have the following code:
alert( [[0,1],[1,0]].indexOf([0,1]) );
And even though the array [0,1] is an element of the two-dimensional array, I get a value of '-1' returned. What have I done wrong in life?
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indexOf returns -1 if the value pair does not exist.Matt Greenberg– Matt Greenberg2015-12-09 04:15:24 +00:00Commented Dec 9, 2015 at 4:15
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1Possible Duplicate of indexOf syntax for multidimensional arrays? or better Javascript 2d array indexofTushar– Tushar2015-12-09 04:16:55 +00:00Commented Dec 9, 2015 at 4:16
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2 Answers
It doesn't find your element because [0, 1] and [0, 1] are not equal in the same way that 4 and 4 are.
console.log(4 === 4); // true
console.log([0, 1] === [0, 1]); // false
When you do an equality check for things with a type of object, then Javascript uses what's known as reference equality. It checks whether the two objects are actually the same instance.
var a = [0, 1];
var b = [1, 0];
var arr = [a, b];
console.log(arr.indexOf(a)); // 0
console.log(a === arr[0]); // true
Alternatively you can write your own search function using a deep equality check.
function deepSearch(arr, element) {
for(var index = 0; index < arr.length; index++) {
if(deepEqual(arr[index], element)) {
return index;
}
}
return -1;
}
Comments
Short answer: Because [0,1] === [0,1] is false.
According to .indexOf documentation,
indexOf()comparessearchElementtoelementsof the Array using strict equality (the same method used by the ===, or triple-equals, operator).
You can use a trick and serialize your subarrays and target item.
It works, because [0,1] !== [0,1], but "[0,1]" === "[0,1]":
Array.prototype.indexOfForArrays = function(search)
{
var searchJson = JSON.stringify(search); // "[0,1]"
var arrJson = this.map(JSON.stringify); // ["[3,4]", "[0,1]", "[1,0]"]
return arrJson.indexOf(searchJson);
};
document.body.innerText = [[3,4], [0,1], [1,0]].indexOfForArrays([0,1]); There are some other methods. This Stackoverflow question may be useful.
answered Dec 9, 2015 at 4:13
Yeldar Kurmangaliyev
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