How to select the middle of an array?

Question

I thought I could use

$ [1,2,3,4,5].splice((this.length / 2), 1)[0]

but it gives me

$ 1 

I tried

$ [1,2,3,4,5].splice(function() { return this[this.length / 2, 1]})

but it gives me

[ 1, 2, 3, 4, 5 ]

I'm looking for a solution that gives me an integer and for even arrays is the lower of the two, e.g.

[1,2,3,4] givees 2
[1,2,3,4,5] gives 3
[1,2,3,4,5,6] gives 3
[1,2,3,4,5,6,7] gives 4

Answer 1

The issue is with this reference. Try this:

console.log(getMiddle([1,2,3,4]));
console.log(getMiddle([1,2,3,4,5]));
console.log(getMiddle([1,2,3,4,5,6]));
console.log(getMiddle([1,2,3,4,5,6,7]));

function getMiddle(arr){
     return arr.splice(Math.floor((arr.length-1) / 2), 1)[0]
}

However, As @jonrsharpe 's comment states, splicing a single-element array from an index to the same index plus one then getting the first value in the result creates a redundant array. A better way to get the middle element would be the following:

console.log(getMiddle([1,2,3,4]));
console.log(getMiddle([1,2,3,4,5]));
console.log(getMiddle([1,2,3,4,5,6]));
console.log(getMiddle([1,2,3,4,5,6,7]));

function getMiddle(arr){
     return arr[Math.floor((arr.length - 1) / 2)];
}

Answer 2

You cannot use this as a parameter because this is supposed to be called inside functions, whereas splice accept as parameters integers. If you really want to use this you may use a prototype. Use Math.floor function since arrays indexes only accept integers, and Math.floor rounds up to the lowest integer (ex: Math.floor(2.5) === 2).

Array.prototype.getMiddle = function () {
  return this[Math.floor(this.length/2)]
}

console.log([1,2,3,4,5].getMiddle()) // 3

The above function only works when the length of the array is an odd number, since arrays whose length is an even number do not have "middle" element.

If you want to check if the array has a middle

Array.prototype.getMiddle = function () {
  return (this.length % 2) ? this[Math.floor(this.length/2)] : null
}

console.log([1,2,3,4,5].getMiddle()) // 3
console.log([1,2,4,5].getMiddle()) // null

Alternative solutions:

var arr = [1,2,3,4,5]

var middleEl = arr[Math.floor(arr.length/2)] 

console.log(middleEl) // 3

If you want to use splice

var arr = [1,2,3,4,5]

var middleEl = arr.splice((arr.length / 2), 1)[0]

console.log(middleEl)

If you want a function

console.log(middleEl([1,2,3,4,5])) //3
console.log(middleEl([1,2,4,5])) //null

function middleEl (arr) {
   return (arr.length % 2) ? arr[Math.floor(arr.length/2)] : null
}

Answer 3

You should use something like that.

var data, remaining, hold, result;
data = ["1","2","3","4","5","6","7","8", "9"];
remaining = data.length % 2;
hold = Math.floor(data.length / 2);
result = data[(remaining + hold - 1)];
document.write(result);

Answer 4

let arr = [ 1, 2, 3, 4, 5 ]
let len = arr.length;
let mid = Math.floor(len / 2);
console.log(arr[mid]);
// or
console.log(arr.slice(mid, mid + 1));

or if you want the middle two, you can do mid + 2 using a var that tests to see if the length is even.

Answer 5

You could create a prototype for getting the middle element/s.

Array.prototype.middle = function () {
    const
        half = this.length >> 1,
        offset = 1 - this.length % 2;
    
    return this.slice(half - offset, half + 1);
};

console.log([1, 2, 3, 4, 5].middle());    // [3]
console.log([1, 2, 3, 4, 5, 6].middle()); // [3, 4]
console.log([1, 2, 3, 4].middle());       // [2, 3]

.as-console-wrapper { max-height: 100% !important; top: 0; }

Answer 6

Why not simply, assuming a.length > 0:

const a = [1, 2, 3, 4, 5]
console.log(a[(a.length - 1) >> 1])
const b = [1, 2, 3, 4, 5, 6]
console.log(b[(b.length - 1) >> 1])

I think this should be a fairly fast way of doing it. The >> operator is an integer shift, which divides the number by two - ignoring decimals.