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public:how_parkrun_volunteers_sort_barcodes_-_a_computer_scientist_s_perspective [2018/12/28 03:06] – fangfufupublic:how_parkrun_volunteers_sort_barcodes_-_a_computer_scientist_s_perspective [2018/12/28 11:23] (current) – fangfufu
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 ====== How Parkrun volunteers sort barcodes - a computer scientist's perspective ====== ====== How Parkrun volunteers sort barcodes - a computer scientist's perspective ======
-On the Christmas day of 2018, I volunteered at Norwich Parkrun. Towards the end, I ended up helping out with sorting the plastic barcodes. I find the whole process interesting. This is because sorting algorithm is an essential part of computer science curriculum [(https://en.wikipedia.org/wiki/Sorting_algorithm#History)]. I do have a special connection to sorting algorithm - I bumped into Sir Charles Antony Richard Hoare FRS FREng [(https://en.wikipedia.org/wiki/Tony_Hoare)][(https://www.fangfufu.co.uk/wiki/doku.php?id=public:bumping_into_sir_tony_hoare_on_the_day_before_i_learnt_quicksort)], the inventor of quicksort algorithm [(https://en.wikipedia.org/wiki/Quicksort)], the day before I was formally taught quicksort for the second time ((I was taught it once in A-Level Maths D1 module when I was a Year 12 student in Ashmole School, London.)) as a computer science undergrad in University of York.+On the Christmas day of 2018, I volunteered at Norwich Parkrun. Towards the end, I ended up helping out with sorting the plastic barcodes. I find the whole process interesting. This is because sorting algorithm is an essential part of computer science curriculum [(https://en.wikipedia.org/wiki/Sorting_algorithm#History)]. I do have a special connection to sorting algorithm - I bumped into Sir Charles Antony Richard Hoare FRS FREng [(https://en.wikipedia.org/wiki/Tony_Hoare)][(https://www.fangfufu.co.uk/wiki/doku.php?id=public:bumping_into_sir_tony_hoare_on_the_day_before_i_learnt_quicksort)], the inventor of quicksort algorithm [(https://en.wikipedia.org/wiki/Quicksort)], the day before I was formally taught quicksort for the second time [(I was taught it once in A-Level Maths D1 module when I was a Year 12 student in Ashmole School, London.)] as a first year computer science undergrad in University of York.
  
 Sorting numbers inside a computer is a bit different to sorting objects in physical world. This is mainly because the uniform cost model does not apply in the physical world [(costmodel > https://en.wikipedia.org/wiki/Analysis_of_algorithms#Cost_models)]. However some of the concepts in algorithm analysis can still be applied to physical world, for example time complexity and space complexity [(https://www.cs.utexas.edu/users/djimenez/utsa/cs1723/lecture2.html)].  Sorting numbers inside a computer is a bit different to sorting objects in physical world. This is mainly because the uniform cost model does not apply in the physical world [(costmodel > https://en.wikipedia.org/wiki/Analysis_of_algorithms#Cost_models)]. However some of the concepts in algorithm analysis can still be applied to physical world, for example time complexity and space complexity [(https://www.cs.utexas.edu/users/djimenez/utsa/cs1723/lecture2.html)]. 
  
-In this blog post, we analyse the algorithm which Parkrun volunteers use to sort barcodes, using some concepts from computer science.+In this blog post, we analyse the algorithm which Parkrun volunteers use to sort barcodes, using some concepts from computer science. This blog post is written in such a way so you can follow it, even if you have not formally studied computer science. 
 + 
 +In short, Parkrun uses bucket sort to sort their barcodes after each event. I do not think I have encountered an implementation of bucket sort on computers, yet I was treated with a real life implementation of bucket sort on Christmas day.
  
 ===== Analysis of algorithms  ===== ===== Analysis of algorithms  =====
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 The first stage establishes a partial ordering [(https://en.wikipedia.org/wiki/Partially_ordered_set)] of the original data structure (all of the barcodes) - there is ordering amongst the buckets, but there is no ordering within each bucket. To establish total ordering [(https://en.wikipedia.org/wiki/Total_order)], each bucket need to be sorted using comparison sort.   The first stage establishes a partial ordering [(https://en.wikipedia.org/wiki/Partially_ordered_set)] of the original data structure (all of the barcodes) - there is ordering amongst the buckets, but there is no ordering within each bucket. To establish total ordering [(https://en.wikipedia.org/wiki/Total_order)], each bucket need to be sorted using comparison sort.  
  
-==== Sorting individual buckets ====+==== Sorting individual buckets using insertion sort ====
 Different worker threads (volunteers) tend to use different sorting algorithm. Personally I use insertion sort, which is a comparison sort.  Different worker threads (volunteers) tend to use different sorting algorithm. Personally I use insertion sort, which is a comparison sort. 
  
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 However there are some physical optimisation which I made. I collapsed consecutive sorted barcodes into clusters. This is because physically inserting a barcode involves moving all the adjacent barcodes, which takes quite a bit of effort on a rough surface. The two figures below illustrate what I meant:  However there are some physical optimisation which I made. I collapsed consecutive sorted barcodes into clusters. This is because physically inserting a barcode involves moving all the adjacent barcodes, which takes quite a bit of effort on a rough surface. The two figures below illustrate what I meant: 
  
-<columns 100% - - >+<columns 100% 50% 50% >
 <WRAP centeralign> <WRAP centeralign>
 //Uncollapsed barcodes, they became a bit unwieldy to shuffle around. // //Uncollapsed barcodes, they became a bit unwieldy to shuffle around. //
 +
 +{{:public:parkrun:20181225_102455.jpg?400}}
 </WRAP> </WRAP>
  
-{{ :public:parkrun:20181225_102455.jpg?400 |}} 
 <newcolumn> <newcolumn>
 <WRAP centeralign> <WRAP centeralign>
-//Partially collapsed clusters of consecutive barcodes, it was much easier to perform insertion. // +//Partially collapsed clusters of consecutive barcodes, this made it much easier to perform insertion. //
-</WRAP>+
  
-{{ :public:parkrun:20181225_103446.jpg?400 |}}+{{:public:parkrun:20181225_103446.jpg?400}} 
 +</WRAP>
 </columns> </columns>
  
 Preallocation of enough empty space for the missing barcodes should help with the problem as well - that way you don't need to shuffle those out-of-place barcodes.   Preallocation of enough empty space for the missing barcodes should help with the problem as well - that way you don't need to shuffle those out-of-place barcodes.  
  
-==== Conclusion ====+===== Conclusion =====
 I quite enjoyed participating barcode sorting. It is quite of interesting to observe a physical implementation of bucket sort. A lot of computer algorithms are inspired by real life processes. I think perhaps the bucket sort algorithm you learn from textbooks is the abstraction of real life bucket sort process. After all, Wikipedia does not say who came up with bucket sort [(bucketsort)]. It really does make me think - a lot of assumptions in the physical world do not apply in computers, a lot of assumptions that work in computers do not apply in real life. If real life processes can inspire computer algorithms, then surely computer algorithms can inspire real life processes.   I quite enjoyed participating barcode sorting. It is quite of interesting to observe a physical implementation of bucket sort. A lot of computer algorithms are inspired by real life processes. I think perhaps the bucket sort algorithm you learn from textbooks is the abstraction of real life bucket sort process. After all, Wikipedia does not say who came up with bucket sort [(bucketsort)]. It really does make me think - a lot of assumptions in the physical world do not apply in computers, a lot of assumptions that work in computers do not apply in real life. If real life processes can inspire computer algorithms, then surely computer algorithms can inspire real life processes.  
  
-==== Further readings ====+===== Further readings ===== 
 +There are other topics which link computer science into the way the physical world works, for example operational research [(https://en.wikipedia.org/wiki/Operations_research)]. There was a time which all computation were performed by physical objects, to explore this topic, have a look at analogue computers [(https://en.wikipedia.org/wiki/Analog_computer)]. Finally, there have been works on explaining the limitation of computation using physical phenomenons, to explore this topic, have a look at [(Limits on Efficient Computation in the Physical World - https://www.scottaaronson.com/thesis.pdf)] and [(NP-complete Problems and Physical Reality - https://www.scottaaronson.com/papers/npcomplete.pdf)]
  
  
public/how_parkrun_volunteers_sort_barcodes_-_a_computer_scientist_s_perspective.1545966369.txt.gz · Last modified: 2018/12/28 03:06 by fangfufu