JavaScript Sorting Arrays

Sorting an Array

The sort() method sorts an array alphabetically:

Reversing an Array

The reverse() method reverses the elements in an array.

Chủ Đề Bài Viết: Sort javascript

You can use it to sort an array in descending order:

Numeric Sort

By default, the sort() function sorts values as strings.

This works well for strings (“Apple” comes before “Banana”).

However, if numbers are sorted as strings, “25” is bigger than “100”, because “2” is bigger than “1”.

Because of this, the sort() method will produce incorrect result when sorting numbers.

You can fix this by providing a compare function:

Use the same trick to sort an array descending:

The Compare Function

The purpose of the compare function is to define an alternative sort order.

The compare function should return a negative, zero, or positive value, depending on the arguments:

When the sort() function compares two values, it sends the values to the compare function, and sorts the values according to the returned (negative, zero, positive) value.

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If the result is negative a is sorted before b.

If the result is positive b is sorted before a.

If the result is 0 no changes are done with the sort order of the two values.

Example:

The compare function compares all the values in the array, two values at a time (a, b).

When comparing 40 and 100, the sort() method calls the compare function(40, 100).

The function calculates 40 – 100 (a – b), and since the result is negative (-60), the sort function will sort 40 as a value lower than 100.

You can use this code snippet to experiment with numerically and alphabetically sorting:

Sorting an Array in Random Order

The Fisher Yates Method

The above example, array.sort(), is not accurate, it will favor some numbers over the others.

The most popular correct method, is called the Fisher Yates shuffle, and was introduced in data science as early as 1938!

In JavaScript the method can be translated to this:

Find the Highest (or Lowest) Array Value

There are no built-in functions for finding the max or min value in an array.

However, after you have sorted an array, you can use the index to obtain the highest and lowest values.

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Sorting ascending:

Sorting descending:

Using Math.max() on an Array

You can use Math.max.apply to find the highest number in an array:

Math.max.apply(null, [1, 2, 3]) is equivalent to Math.max(1, 2, 3).

Using Math.min() on an Array

You can use Math.min.apply to find the lowest number in an array:

Math.min.apply(null, [1, 2, 3]) is equivalent to Math.min(1, 2, 3).

My Min / Max JavaScript Methods

The fastest solution is to use a “home made” method.

This function loops through an array comparing each value with the highest value found:

This function loops through an array comparing each value with the lowest value found:

Sorting Object Arrays

JavaScript arrays often contain objects:

Even if objects have properties of different data types, the sort() method can be used to sort the array.

The solution is to write a compare function to compare the property values:

Comparing string properties is a little more complex:

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Test Yourself With Exercises

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