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An introduction to sorting

cardsThe term 'sorting' in programming is used to describe putting a collection of data into an order of some kind. You could sort all of the students in your class in order of date of birth, height, exam marks in the last test or alphabetically. When you play some games of cards, you are dealt a set of cards and you have to put them in some kind of order, perhaps from high to low, or in order of suits first and then low to high card values. It is important to know how to sort data in programming because it often speeds up processing data; processing data that is sorted first is often a lot faster than working on and processing data that is unsorted.

How data is sorted is quite an important area in Computer Science. Lots of sorting algorithms have been written to sort data. These 'algorithms' are simply very precise descriptions of how you can take a set of data items and sort them. Once you have the algorithm, you can then convert it into any programming language you are skilled in. Some of these algorithms are very complicated and in fact, too complicated for just a few data items that need sorting. Other sorting algorithms are very simple and are great for small sets of data, but take a very long time to sort data if the sets of data are large. And then there are compromise sorting algorithms. These are a balance between the advantages and disadvantages of the best and the worst sorting algorithms. How fast a sorting algorithm is for a particular set of data is very important for programmers as they want their programs to run as fast as possible.

There are two things we should know about when sorting data. The first thing we need to understand is that to sort data elements, we need to compare them. For example, if I had the two pieces of data 45 and 79, I need to compare them to put them in an order. I need to ask a question like "Is the first piece of data greater than the second" or "Is the first piece of data less than the second". If I have five pieces of data e.g. 42, 76, 5, 49 and 29, then I need to ask the same sort of questions, but again, I can only do this for a pair of data elements. I have to e.g. compare 42 and 76, and then compare 42 and 5, and then compare 42 and 49 and so on.

The second thing we need to understand is that when we compare data elements, and when we have to swap them around because they are in the wrong order, this takes programming time and ultimately, slows down the whole program. What we want to aim for is to sort our data with as few comparisons as possible and by doing as few swaps of data as possible.

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