I discovered the same difference between M.list() and list(M) when formulating my reply. It seems that list(M) is the same as M.rows() rather than M.list(), but I don't know why it was implemented this way. It may just be an accident, since list(M) calls the python function list() and what that does with an object depends on the object's structure somehow. You can also see from M.rows?? that M.rows() calls list(M).
John On 18 November 2013 09:52, Eileen Ee <eileen...@gmail.com> wrote: > Thanks, John! > > That worked well! On a note, before I saw your reply, I used list(M) when I > tried to convert the matrix into a list but list(M) contains segregation in > the list. > > Example: > sage: m = matrix(ZZ, 2, 3, [1,0,1,0,1,1]) > sage: list(m) > > [(1, 0, 1), (0, 1, 1)] > > sage: m.list() > > [1, 0, 1, 0, 1, 1] > > > What I wanted is a list without the segregation, ie. m.list(), not list(m). > I wonder why these two commands produce different results... > > > Thanks, John! You have been a great help! > > > Cheers, > > Eileen > > > On Friday, 15 November 2013 17:12:06 UTC+8, John Cremona wrote: >> >> Try this: >> >> sage: M = random_matrix(GF(2),4,5) >> sage: len([a for a in M.list() if a]) >> 12 >> >> Here M.list() is a list of all the entries, we select the nonzero ones >> and count. >> >> John Cremona >> >> On 15 November 2013 08:25, Eileen Ee <eile...@gmail.com> wrote: >> > Hi everyone, >> > >> > I want to count the number of non-zero entries in a matrix but I can't >> > find >> > a Sage command to do this. Instead, I found a NumPy command >> > numpy.count_nonzero to do it. >> > >> > I tested it in the online Sage Cell server: >> > https://sagecell.sagemath.org/ >> > The code goes like this: import numpy as np >> > mm = matrix(ZZ, 2, 3, >> > [1,0,2,0,0,0]) >> > print mm >> > print np.count_nonzero(mm) >> > >> > It worked in the Sage Cell Server. However, when I tried it out in Sage >> > v5.12 in Linux. There is an error message: " 'module' object has no >> > attribute 'count_nonzero' ". Also, when I typed numpy.<tab> to see all >> > possible commands, numpy.count_nonzero does not appear. It seems as >> > though >> > there is no such command. >> > >> > I am willing to use other simple commands as long as I get to count the >> > nonzero entries of a matrix. Perhaps someone can help me with this... >> > >> > Thanks! >> > >> > Cheers, >> > Eileen. >> > >> > -- >> > You received this message because you are subscribed to the Google >> > Groups >> > "sage-support" group. >> > To unsubscribe from this group and stop receiving emails from it, send >> > an >> > email to sage-support...@googlegroups.com. >> > To post to this group, send email to sage-s...@googlegroups.com. >> > Visit this group at http://groups.google.com/group/sage-support. >> > For more options, visit https://groups.google.com/groups/opt_out. > > -- > You received this message because you are subscribed to the Google Groups > "sage-support" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sage-support+unsubscr...@googlegroups.com. > To post to this group, send email to sage-support@googlegroups.com. > Visit this group at http://groups.google.com/group/sage-support. > For more options, visit https://groups.google.com/groups/opt_out. -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To post to this group, send email to sage-support@googlegroups.com. Visit this group at http://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/groups/opt_out.
