It's nuanses, I'd say "i, j and values". I also wanted to contrast "(perhaps i,.j and value as *two* map files)", because accessing i and j separately is convenient and splitting them from one file will result in unmapped copies.
--- Roger Hui <[EMAIL PROTECTED]> wrote: > Roger: Better to just map i and j and values separately > Oleg: Or maybe three mapped files: i, j, values. > > What is the difference between the two descriptions? > > > > ----- Original Message ----- > From: Oleg Kobchenko <[EMAIL PROTECTED]> > Date: Thursday, January 10, 2008 2:59 > Subject: Re: [Jgeneral] table (i,j,value) to matrix > To: General forum <[email protected]> > > > --- Roger Hui <[EMAIL PROTECTED]> wrote: > > > Better to just map i and j and values separately > > > (perhaps i,.j and value as two map files), and apply your > > > iterative methods to these. > > > > Or maybe three mapped files: i, j, values. > > Then access to the matrix is simply relational. > > See http://www.jsoftware.com/jwiki/DB/Flwor > > > > i.3 > > 4 NB. matrix > > 0 1 2 3 > > 4 5 6 7 > > 8 9 10 11 > > (#: i.@(*/)) 3 4 NB. index odometer > > 0 0 > > 0 1 > > 0 2 > > 0 3 > > 1 0 > > 1 1 > > 1 2 > > 1 3 > > 2 0 > > 2 1 > > 2 2 > > 2 3 > > 'r c'=. |:(#: i.@(*/)) 3 4 > > v=. ,@i. 3 4 > > > > r,.c,.v NB. relational form > > 0 0 0 > > 0 1 1 > > 0 2 2 > > 0 3 3 > > 1 0 4 > > 1 1 5 > > 1 2 6 > > 1 3 7 > > 2 0 8 > > 2 1 9 > > 2 2 10 > > 2 3 11 > > 1 = > > r NB. row 1 mask > > 0 0 0 0 1 1 1 1 0 0 0 0 > > v #~ > > 1=r NB. SQL: select v where r=1 > > 4 5 6 7 > > 1 2 =/ > > r NB. rows 1 2 mask > > 0 0 0 0 1 1 1 1 0 0 0 0 > > 0 0 0 0 0 0 0 0 1 1 1 1 > > v #~ 1 2 =/ r NB. > > rows 1 2 value > > 4 5 6 7 > > 8 9 10 11 > > > > 1 = > > c NB. column 1 mask > > 0 1 0 0 0 1 0 0 0 1 0 0 > > v #~ 1 = > > c NB. etc ... > > 1 5 9 > > > > v #~ c = 1 > > 1 5 9 > > 1 3 =/ c > > 0 1 0 0 0 1 0 0 0 1 0 0 > > 0 0 0 1 0 0 0 1 0 0 0 1 > > v #~ 1 3 =/ c > > 1 5 9 > > 3 7 11 > > > > > > (t#r),.(t#c),.v#~t=. 0=4|v NB. 4 multiple > > 0 0 0 > > 1 0 4 > > 2 0 8 > > > > (~.r) ,. > > r+//.v NB. sum by rows > > 0 6 > > 1 22 > > 2 38 > > +/"1 i.3 4 > > 6 22 38 > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ____________________________________________________________________________________ Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
