From: RichardOnRails Date: 2009-03-20T09:57:19+09:00 Subject: Re: Complex sort of matrix possible, e.g. like Excel? On Mar 19, 5:18 pm, Rob Biedenharn wrote: > On Mar 19, 2009, at 4:42 PM, RichardOnRails wrote: > > > > > On Mar 18, 12:31 pm, Rob Biedenharn > > wrote: > >> On Mar 18, 2009, at 1:58 AM, Christopher Dicely wrote: > > >>> Enumerable#sort lets you do this fairly easily with just a pure   > >>> array > >>> of arrays, e.g., to sort the array-of-arrays "arr" by the first   > >>> column > >>> ascending and the second descending: > > >>> arr.sort {|a,b| [a[0]<=>b[0], b[1]<=>a[1]].find {|x| x!=0} || 0} > > >> Not to detract to much from the other responses, but this ought to   > >> be: > > >> arr.sort {|a,b| (a[0] <=> b[0]).nonzero? || b[1] <=> a[1] } > > >> Take a look at what Numeric#nonzero? does.  The docs specifically > >> mention its use when chaining comparisons this way. > > >> Doing arr.sort_by {|a| [a[0], -a[1]] } only works if the second > >> element responds to @- (like any Numeric would, but certainly not > >> String). > > >> -Rob > > >>> On 3/17/09, RichardOnRails   > >>> >>>> wrote: > >>>> Hi, > > >>>> I've got an array of rows (and thus a matrix) created user   > >>>> FasterCSV > >>>> to extract data from a CSV file.  I'd like to sort the matrix on > >>>> column A ascending and, within that, column B descending.  I looked > >>>> at > >>>> Matrix,  but it doesn't seem to address that functionality.  Is   > >>>> there > >>>> a package that does, or do I have to write my own SuperMatrix > >>>> inherited from Matrix? > > >>>> Thanks in Advance, > >>>> Richard > > >> Rob Biedenharn          http://agileconsultingllc.com > >> R...@AgileConsultingLLC.com > > > On Mar 18, 12:31 pm, Rob Biedenharn > > wrote: > >> On Mar 18, 2009, at 1:58 AM, Christopher Dicely wrote: > > >>> Enumerable#sort lets you do this fairly easily with just a pure   > >>> array > >>> of arrays, e.g., to sort the array-of-arrays "arr" by the first   > >>> column > >>> ascending and the second descending: > > >>> arr.sort {|a,b| [a[0]<=>b[0], b[1]<=>a[1]].find {|x| x!=0} || 0} > > >> Not to detract to much from the other responses, but this ought to   > >> be: > > >> arr.sort {|a,b| (a[0] <=> b[0]).nonzero? || b[1] <=> a[1] } > > >> Take a look at what Numeric#nonzero? does.  The docs specifically > >> mention its use when chaining comparisons this way. > > >> Doing arr.sort_by {|a| [a[0], -a[1]] } only works if the second > >> element responds to @- (like any Numeric would, but certainly not > >> String). > > >> -Rob > > >>> On 3/17/09, RichardOnRails   > >>> >>>> wrote: > >>>> Hi, > > >>>> I've got an array of rows (and thus a matrix) created user   > >>>> FasterCSV > >>>> to extract data from a CSV file.  I'd like to sort the matrix on > >>>> column A ascending and, within that, column B descending.  I looked > >>>> at > >>>> Matrix,  but it doesn't seem to address that functionality.  Is   > >>>> there > >>>> a package that does, or do I have to write my own SuperMatrix > >>>> inherited from Matrix? > > >>>> Thanks in Advance, > >>>> Richard > > >> Rob Biedenharn          http://agileconsultingllc.com > >> R...@AgileConsultingLLC.com > > > Hi Rob, > > > Thanks for your response.  I don't want to be an expert on sorting > > matrices.  I just want to get my project working. (Don't we all :-) > > > Here's the essence of what I've got working, confirmed with debugging > > puts'. > > > matrix = [] > > FasterCSV.foreach(selectedCsvFile, :headers => false) do |row| > >    matrix << row > > end > > > I want (in Excel terms) the matrix sorted on column B asc. and within > > that col. I asc.  Both columns are textual.  Based on your guidance, I > > added the line: > > > sortedMatrix = matrix.sort {|a,b| [a[1]<=>b[1], a[8] <=> b[8]]} > > > Ruby gave me a syntax error: > > ProcessExports.rb:130:in `sort': undefined method `>' for [-1, > > 1]:Array (NoMethodError) > > > I'm hoping the problem is that I'm invoking Array::Sort rather than > > Enumerable::Sort but nothing my deteriorating brain could devise > > worked.  Any ideas. > > > Best wishes, > > Richard > > Well, my guidance was: >    arr.sort {|a,b| (a[0] <=> b[0]).nonzero? || b[1] <=> a[1] } > > Which translates to your: >    sortedMatrix = matrix.sort {|a,b| (a[1]<=>b[1]).nonzero? || a[8]   > <=> b[8] } > > You might also need: >    matrix << row.to_a > or >    matrix << row.fields > in your loop, but a FasterCSV::Row probably behaves sufficiently like   > an Array to sort properly. Whether it continues to behave later (when   > you *really* need an Array), may resolve the question of whether you   > need to call #to_a or #fields on your row. > > Real code will always get you a better answer that pseudo-code. > > If you meant for either sort on Col.B or Col.I to be *descending*,   > then swap the a and b in the appropriate expression. (Your original   > question had the secondary sort descending, but the latest [with   > code ;-)] says "col. I asc.") > > -Rob > > Rob Biedenharn          http://agileconsultingllc.com > R...@AgileConsultingLLC.com Rob, Thank you very much for hanging in there with me until the fog lifted. I thought about your advice and managed to mangle it. If I hadn't been such a "wise guy", I could have translated your original advice as you did and been on my way. Regarding the asc/desc on the I col., I changed my mind midway and decided my app requires asc. on I. But I have a final question: I thought your expression had a flaw because, in my view, "(a[1]<=>b[1]).nonzero?", if true, should cause the block to return true rather than plus or minus. So I concocted: sortedMatrix = matrix.sort {|a,b| (v = a[1]<=>b[1]).nonzero? ? v : (a [8] <=> b[8] )} which works. But yours works, too. So my understanding of how block evaluation works when invoked by a calling function is flawed. Do you have a simple explanation of the flaw in my thinking, or can you point me to a relevant online tutorial on this? But don't trouble yourself on this; it's only icing on the cake. Thank you very much for the pains you took to get me going again. Very best wishes, Richard