In other words, not only are loops "built into some verbs (+/ -/)" but they are built into all verbs. But we don't really think of them as having loops. Ken Iverson told the following anecdote: In J we say, "move the army from Boston to New York"; in a scalar language you'd say for i in range (0,n) move soldier i from Boston to New York. Do you think of "move" as having a loop built in?
On Sat, Feb 15, 2014 at 9:15 AM, Roger Hui <rogerhui.can...@gmail.com>wrote: > > ...loops? From what I've seen loops are built into some verbs (+/ -/ > > etc), but what if you wanted to do say: add every number in the > > vector, but for every number add 2.91, then divide that by 0.4? > > In python: > > range() generates a list of numbers from 0 to 9. > > for x in range(0,10) > > y += (x + 2.91) / 0.4 > > In J: > ((i. 10) + 2.91) % 0.4 > or > (2.91 + i. 10) % 0.4 > or > 0.4 %~ 2.91 + i. 10 > > > > > On Sat, Feb 15, 2014 at 9:04 AM, Lee Fallat <ircsurfe...@gmail.com> wrote: > >> Thanks for the explanation Raul. >> >> I think I understand now that string manipulation in J is >> non-trivial...I was following right up until the very last J sentence >> ( 'hi',:&.(-&(a.i.'*'))&.(a.&i.)'there'), mostly because I still only >> know a few verbs. I am starting to think J is either not for me, or my >> way of thinking really needs to change for this language. There are so >> many things that would seem straight forward in traditional languages >> than J, but I will have to see! >> >> Some examples of what I'm thinking of would be difficult or different in >> J: >> Passing 3 or more parameters to a verb >> Turning a vector into a list of arguments >> >> ...loops? From what I've seen loops are built into some verbs (+/ -/ >> etc), but what if you wanted to do say: add every number in the >> vector, but for every number add 2.91, then divide that by 0.4? >> In python: >> range() generates a list of numbers from 0 to 9. >> for x in range(0,10) >> y += (x + 2.91) / 0.4 >> One other thing is interacting with the operating system...How do I >> check to see if files, or even directories exist? Can you create >> directories, or change permissions of files with J? The scope of J >> seems to be very constrained to mathematics. It would be nice to use J >> as a system programming language! Are there any examples of people >> doing these things? >> >> Anyways, I apologize for being off-topic, but just some things I've >> been thinking about. Like I said I still have to get through some more >> learning material. >> >> Regards, >> >> Lee >> >> >> >> On Sat, Feb 15, 2014 at 11:37 AM, Raul Miller <rauldmil...@gmail.com> >> wrote: >> > Conceptually speaking, J has three "atomic data types": >> > >> > Numeric >> > Literal >> > Boxed >> > >> > Numeric types support arithmetic: 1+1 >> > Literal types are what might be called character types in other >> languages. >> > (ascii or unicode) >> > Boxed types are what might be called reference types in other languages. >> > >> > J tries to treat numeric types as mathematical arithmetic entities. It's >> > not perfect, and involves tradeoffs but it does a pretty good job at >> being >> > useful and educational while still offering decent performance with a >> > relatively compact implementation. Also, J booleans are numeric and I >> > vastly prefer this approach (which fits my understanding of the history >> of >> > booleans) over the convention of enshrining arbitrary implementation >> > limitations. >> > >> > You cannot perform arithmetic directly on literals but you can, for >> > example, compare an ascii 'A' with a unicode 'A' and get a literally >> > correct answer. (However, unicode also includes an open ended set of >> rules >> > and extensions and if you want those you will probably need to implement >> > them yourself. To avoid open-ended arguments about these issues its >> perhaps >> > better to refer to this type of data as 'literal' rather than >> 'character'.) >> > >> > Boxes take an arbitrary array and "puts it in a box" - you get a single >> > thing which can be treated something like a literal or a number. >> > >> > You cannot mix these three types in the same array, but if you put >> > something in a box you can put the box in an array of boxes. >> > >> > Anyways... >> > >> > For some contexts you might use a list of characters (excuse me: I mean >> > literals) to represent a string. For other contexts you might want to >> put >> > that list of characters in a box. If you arrange your strings as a two >> > dimensional array they will all be padded (with spaces) to match the >> length >> > of the longest one. >> > >> > Actually, in some contexts you might want to use a list of numbers to >> > represent a string. Sometimes arithmetic is handy. >> > >> > Put differently, J does not actually have a "string" data type. But you >> can >> > represent them using arrays. >> > >> > Examples: >> > >> > 'hello' >> > hello >> > 'hello';'there' >> > ┌─────┬─────┐ >> > │hello│there│ >> > └─────┴─────┘ >> > 'hi',:'there' >> > hi >> > there >> > 'hi',:&.(-&(a.i.'*'))&.(a.&i.)'there' >> > hi*** >> > there >> > >> > In that last example, I made the padding character by '*' rather than ' >> '. >> > I did this by combining the two strings as numbers rather than literals. >> > The padding value for numbers is zero. But if I had stopped there I >> would >> > have gotten ascii nulls for my padding. So I also combined them under >> > subtracting by the numeric value for '*'. >> > >> > Under performs the reverse transform for the result (of the transform >> that >> > it performed from the arguments), >> > http://www.jsoftware.com/jwiki/Essays/Under >> > >> > I hope this makes sense. >> > >> > Thanks, >> > >> > -- >> > Raul >> > >> > On Sat, Feb 15, 2014 at 10:31 AM, Lee Fallat <ircsurfe...@gmail.com> >> wrote: >> > >> >> Thank you all for your kind replies! And to those saying how I should >> >> really use awk for this job- I know, I was just curious! I am very >> >> impressed by the variance in answers, and how different J really is >> >> compared to other languages. >> >> >> >> Thanks again, >> >> >> >> Lee >> >> >> >> P.S. As for the input, just numbers was fine. I'm curious though what >> >> J does when it encounters strings (and numbers!). I figured reading >> >> through the books offered on the wiki will explain this. (+/ "hello" >> >> "world" 100 = what? :) >> >> >> >> On Sat, Feb 15, 2014 at 10:20 AM, Jim Russell <jimsruss...@yahoo.com> >> >> wrote: >> >> > I love AWK; it (and perl) have saved my bacon many times. If your >> >> problem involves processing fields within lines of an I/O stream in a >> *nix >> >> environment, of course you or I should use AWK. Particularly me, since >> I'd >> >> never be given a processing task involving more math than a "gozinta" >> or >> >> takeaway, much less anything involving polynomials, natural logs, verb >> >> inverses, factorials, ranks above 3, and a whole bunch of stuff that J >> >> would do for me if only I understood what it was. >> >> > >> >> > (I would also pick AWK if I had only 5 minutes to learn a new >> language.) >> >> > >> >> > But had AWK never been invented (shudder), and I needed to write it, >> >> would I use J? Well, not me, but I know some folks here that might >> knock it >> >> out using J in an afternoon or two. >> >> > >> >> >> On Feb 14, 2014, at 9:51 PM, Lee Fallat <ircsurfe...@gmail.com> >> wrote: >> >> >> >> >> >> Hey there, >> >> >> >> >> >> As new user to J (but several years experience with C and Java), I >> >> >> find it very, very interesting. The power of its one liners and >> >> >> mathematical heritage really have me hooked. I was wondering though >> >> >> if it has similar capabilities as awk. What's the equivalent to this >> >> >> awk script in J?: >> >> >> >> >> >> BEGIN { FS=";" } >> >> >> { print $1+$2 } >> >> >> >> >> >> This script sets a FieldSeparator to ;, and then for every "row", >> add >> >> >> the first and second column and prints it. I would like to replace >> awk >> >> >> with J! >> >> >> >> >> >> Thank you, >> >> >> >> >> >> Lee >> >> >> >> >> >> P.S. Excuse me if I've misidentified J sentences. (Sentences -> >> >> statements?) >> >> >> >> ---------------------------------------------------------------------- >> >> >> For information about J forums see >> http://www.jsoftware.com/forums.htm >> >> > >> ---------------------------------------------------------------------- >> >> > For information about J forums see >> http://www.jsoftware.com/forums.htm >> >> ---------------------------------------------------------------------- >> >> For information about J forums see http://www.jsoftware.com/forums.htm >> >> >> > ---------------------------------------------------------------------- >> > For information about J forums see http://www.jsoftware.com/forums.htm >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm > > > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
