A couple years ago, i posted a programing problem, about writing a function that will sort a arbitrarily dimentioned matrix in any possible way to sort it.
Such a function, is rather typical in functional programing languages. I wrote a version in 1999 in perl for practical purposes, since sorting a matrix (i.e. list of lists) is rather common. With this function, i can have a single interface to deal with any list (including list of lists). It is ideal, that a language's function for sort actually are of this generality. (See “What is Expressiveness in a Computer Language”, Xah Lee, 2005. http://xahlee.org/perl-python/what_is_expresiveness.html ) The advantage of such a generality, is that a programer don't need to write a sorting code every time she encounters a list. Anyway, so i wrote it in 1999 in perl for practical purposes, and have used it in industrial coding often. In 2005, while i was learning Python, i wrote a python version as a exercise. Today, i actually need it again, while coding in python. So i looked at my code and spruced up the documentation. Here's the function spec: ---------------- Today we'll write a function that can sort a matrix in all possible ways. Following is the specification. Take a day to see if you can write such a function in your favorite language. Perl and Python solutions are at the end of this page. sort_matrix( matrix, [[n1, s1, d1], [n2, s2, d2], [n3, s3, d3], ...]) returns a sorted matrix by n1 th column, if tie, then by n2 th column ... and so on. The first argument is a list, whose elements are lists of equal lengths. s1, s2, s3... are booleans. If True, then the corresponding column are interpreted as a string and the ordering is lexicographical. d1, d2, d3... are booleans. If True, the sort for the corresponding column are ascending. Example:. myMatrix = [ [3, 99, 'a'], [2, 77, 'a'], [1, 77, 'a'] ]; sort_matrix(myMatrix,[[3,True,True],[2,False,True]]) This means sort by 3th column, regarding it as strings, and in ascending order. If tie, sort by 2th column, regarding it as number, in ascending order. It returns: [[2,77,'a'], [1,77,'a'], [3,99,'a']] ---------------- While reviewing this code, there's something interesting of note. Namely, in my perl solution, the approach is drastically different than the python version. Instead of sorting by looping thru the sorting directives, it parses the directives then generate the complete sort code, then eval it in one shot. This is more of a pure functional approach. I thought it is of interest. The Perl and Python solutions are at: General Function For Matrix Sorting http://xahlee.org/perl-python/sort_matrix.html It would be interesting, to see a python version using the approach i've done in the Perl version, and a Perl version using imperative approach without using eval(). A solution in lisp (emacs lisp, common lisp, scheme) would be relatively trivial, similarly for Haskell and Mathematica. In fact, i think the sort function as specified above are not very useful in practice in these languages to various degress (depending on the lang). Because a functional language usually have powerful, generalized functions and constructs that solve the above in a few trivial lines that are rather ideomatic to the language. Nevertheless, it would be interesting to see a solution in the above languages. For the languages i'm personally involved, a major difficulty would be Java. In my opinion, it would be a very difficult (if not impossible) to construct this sort function Java, C, C++, C#. Xah [EMAIL PROTECTED] ∑ http://xahlee.org/ -- http://mail.python.org/mailman/listinfo/python-list