How to randomly output an array in JavaScript

The need to randomly output arrays often appears in JavaScript development. For example, suppose we have an array that stores a lot of data, and we need to randomly output a part of the data. So, how to achieve this?

The following are several implementation methods:

1. Math.random() method

Math.random() method is a random number provided by JavaScript Generate function. It will return a random number between 0 and 1. We can use this method to generate a random number index, and then use this index to obtain the corresponding element from the original array.

The sample code is as follows:

var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
var randomIndex = Math.floor(Math.random() * arr.length);
console.log(arr[randomIndex]);

In the above code, use the Math.random() method to generate a random number between 0-1, and then multiply it by the length of the array to get a random number. Numeric index, use this index to obtain the corresponding element from the original array.

2. Array.sort() method

Another method is to use the Array.sort() method to randomly sort the array and then output the first few elements of the array . The specific implementation is as follows:

var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
arr.sort(function() { return Math.random() - 0.5 });
console.log(arr.slice(0, 3));

The above code first uses the sort() method to randomly sort the array. The sort() method accepts a comparison function as a parameter. The value returned by the function is less than 0, indicating that the first parameter is ranked Before the second parameter, if the return value is greater than 0, it means that the first parameter comes after the second parameter. Since the function returns a random number, the array will be sorted randomly.

Then use the slice() method to remove the first three elements from the array as the result of random output.

3. Fisher–Yates shuffling algorithm

Fisher–Yates shuffling algorithm, also known as Knuth shuffling algorithm, is an algorithm that randomly arranges elements in an array. Its implementation is as follows:

function shuffleArray(arr) {
  for (var i = arr.length - 1; i > 0; i--) {
    var j = Math.floor(Math.random() * (i + 1));
    var temp = arr[i];
    arr[i] = arr[j];
    arr[j] = temp;
  }
  return arr;
}

var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
console.log(shuffleArray(arr).slice(0, 3));

In the above code, a random position is selected for exchange each time by looping through the array, and finally a randomly arranged array is obtained. Then use the slice() method to remove the first three elements from the array as random output results.

Summary

The above are several common implementation methods, each method has its advantages and disadvantages. For example, the first method is the simplest, but there may be the problem of repeatedly outputting the same element; the second method is relatively random, but the code is a bit lengthy; the third method is a relatively perfect implementation. method, but you need to write a function to encapsulate it.

Developers can choose a suitable method for implementation based on their actual needs. Either way, the ability to randomly output array elements is an important skill in JavaScript development.

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