You have a hammer (pattern matching) and you are requiring that a problem must be solved using a hammer. I solved the same problem with a scalpel.
On Tue, Oct 8, 2013 at 1:49 PM, Richard Gaylord <[email protected]> wrote: > *sorry it took me so long to return to the thread. i've been dealing with > health issues again (my advice is not to develop an autoimmune neurological > disease).* > * > * > *the responses to my question about pattern matching in J really do not > address the matter. the code given by roger* > * > * > > *p,|."1 p > * > * /:~p,|."1 p * > * > * > *is very clever but it does not, as best i can tell, directly employ > pattern matching while my WL code does. * > * > * > *also, it does not start at the same point (use the same input) as the WL > code, nor does it end at the same point (with the same output) as te WL > code. * > * > * > *perhaps it is my fault becuase of the specific example i used but let me > restate it exactly as the corresponding code needs to appear and tn perhaps > the code to accomplish the same task in J can be posted * > * > * > *(but it must have the identical Input [1] and Output [2] as the WL code > (starting with p - which is not the same as society - is not acceptable > (although i can certainly convert society into p in WL). it must start > with society (or whatever you want to call it as long as it has the > identical structure)* > * > * > *Input[1]* > * > * > *society = {{1, {5, 7}}, {2, {}}, {3, {}}, {4, {1, 2}}, {5, {2, 7}}, {6, > {2}}, {7, {8}}, {8, {5}}};* > * > * > *note: becuase of my use of the semi-colon, Input [1] does not return any > Output* > * > * > > *note: the 2nd element in each list in society is not necessarily limited > to an empty list and a 2-element list. it just happened to be that way.* > * > * > > *Input [2]* > > * > * > > *symSoc = society /.* > > * {a_Integer, b_} :> {a, Union[b, Cases[society, {x_, {___, a, ___}} :> > x]]}* > > * > * > > *Output [2]* > > * > * > > *{{1, {4, 5, 7}}, {2, {4, 5, 6}}, {3, {}}, {4, {1, 2}}, {5, {1, 2, 7, > 8}}, {6, {2}}, {7, {1, 5, 8}}, {8, {5, 7}}}* > > * > * > > > *as for roger's question as to what the WL code is doing:* > > * > * > > *we start in society with a list which contains a list * > > *for each person in the system (so if there are 8 people in society, the > list consists of 8 elements, each a list.* > > * > * > > *e.g.. for person A we have **{A, {B,**R,E}} **the first element is the > person's name and the second element in each list is a list of the names of > the friends of A (let's say they are B, R, E).* > > * * > > *using symSoc, we look at the list of each and every person in the system. > specifically, we look at the 2nd element for each person to see if the name > A appears anywhere in another person's list of friends e.g. look at the > list of friends of person D, and if A is in the list, then the name D is > added to the list of friends of A. * > > * > * > > *since it may be that D is already listed as a friend of A, D would appear > twice in the list of of A's friends so we use the Union command to set rid > of the duplicates of names and sort them as well.* > > * > * > > *i hope this explanation is clear (i don't usually explain what what my > code is doing; some of the functions i like to create are nested anonymous > (or pure) functions that are virtually unreadable, even to me a day or so > after i've created them).* > > * > * > > *finally, let me note that anything that can be done in J can be done in WL > and in this case, roger took my example and without using what i call > pattern matching accomplished the same thing. but there are cases where > pattern matching is, if not the only way to go, it is much easier to write > the code for.* > > * > * > > *i hope this explains what's going on and what i' m asking about. if you go > to my note set (available as a pdf at > http://library.wolfram.com/infocenter/MathSource/5216/ you'll find a > tutorial on WL and the last section includes the code above and more code > (i especially like the SocNetFunction i created which is a nested anonymous > function* > > * > * > > *socNetFunction[rule_] := Function[y, Map[rule[Join[{#}, y[[#[[2]] ]] ] ] > &, y] ]* > > * > * > > * > * > > * * > > > > > -- > > *"Those who would sacrifice freedom for security deserve neither." - > Benjamin Franklin* > > > *"I think that the very notion that equations are a good approach to > describing the natural world is a little bizarre." > - Stephen Wolfram* > > * > * > > nested > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
