ASCII, Unicode and alphanumeric lists

Intricacies of native sorting

Using native sorting functions to order lists that contain alphanumeric strings will most of the time yield unexpected results. For example, when using a program to order a list of flights in ascending order, the results are most likely to resemble the following:


Most text editors serve as binary-to-symbol translators. In this case, the above table was typed on a text editor and was stored in some location as a set of ASCII, Unicode or some other type of binary values. The result of sorting that translation is a “lexical” sort meaning that “1006” comes before “289”.

What are ASCII Values?

ASCII stands for American Standard Code for Information Interchange. ASCII is a binary file format that assigns a 7-bit binary value (a string of seven 0s and 1s) to alphanumeric, numeric and some special characters — most keys on the standard keyboard.

ASCII code was first introduced in the early 1960’s and was based on a system used in telegraphy. In ASCII, numbers 0 to 9 are assigned smaller values than upper case letters A to Z, and upper case letters are assigned smaller values than lower case letters a to z.

This type of sorting is efficient for machines and produces reasonable results when using the English alphabet. However, since ASCII is American centric it presents limitations for Asian languages and other languages that contain characters outside of the English alphabet.


Unicode is a newer (1987) standard for representing characters. It also stores characters in binary form, but rather than using only 7-bits, Unicode is based in 16-bit binary values which allows more than 1,000,000 possible character representations (as opposed to ASCII’s 128 character limit). Currently, Unicode includes characters from most popular languages and preserved the order of the first 128 ASCII characters. Although many languages were originally based on ASCII (Python, R, C and C++), Unicode has been implemented in many recent technologies and supported by most languages.

When sorting lists that allow alphanumeric characters on a string, in most programs, is necessary to define a custom sorting algorithm that does not relay in the order of individual character’s codes - some places refer to it as “natural sorting.” A comprehensive list of natural sorting algorithms in most languages can be found here.