In J, I can update a subset of an array in place according to some predicate, like so: y (k}~) |. y {~ k =. I. '123' e.~ y =. '[1.2.3]' [3.2.1] I realize I can factor out a conjunction here, bu...

I'm working through the J primer, and getting stuck when it comes to the load command. In particular, there are times when the next step in a tutorial is load 'foo' and I'll get an error like the ...

Disclosure This is a "general" question, perhaps without a specific answer, but it is not intended as a flame war. I would really like some information before embarking on my project. I hav...

I am reading a review to compare Mathematica to APL/J. One question raised in the article seems very interesting to me: Is Mathematica really the way to go to express our creative thoughts...

For the evolution from APL to J, What's the motivation to introduce fork? I guess it is nice to have (+/ % #) for calculating the average, but it also makes it harder to read longer verb train. Fac...

I've just started learning J, which is very interesting, but I was wondering what kind of language it is exactly, in relation to common paradigms and classifications. For example, you could say tha...

I've been using J for a few months now, and I find that reading unfamiliar code (e.g. that I didn't write myself) is one of the most challenging aspects of the language, particularly when it's in t...

As title says, I don't understand why f^:proposition^:_ y is a while loop. I have actually used it a couple times, but I don't understand how it works. I get that ^: repeats functions, but I'm conf...

Suppose a boxed matrix containing various types: matrix =: ('abc';'defgh';23),:('foo';'bar';45) matrix +---+-----+--+ |abc|defgh|23| +---+-----+--+ |foo|bar |45| +---+-----+--+ And a column d...

I want to put the operation which takes all the items in a list which are greater than 2 into a pointless (as in not explicitly capturing the argument in a variable) function in J. I wanted to do t...

Given I have a boxed array with shape 4 3 v =. 4 3$'x1'; 'y1'; 'z1'; 'x2'; 'y2'; 'z2'; 'x3'; 'y3'; 'z3' v NB. +--+--+--+ NB. |x1|y1|z1| NB. +--+--+--+ NB. |x2|y2|z2| NB. +--+--+--+ NB. |x3|y3|z3| ...

In the console, typing a single verb without parameters will print its content: tolower 3 : 0 x=. I. 26 > n=. ((65+i.26){a.) i. t=. ,y ($y) $ ((x{n) { (97+i.26){a.) x}t ) That's nice for de...

How does one do array accesses in the J programming language? For example, using C++ as my pseudocode language: int M [100]; // declare an array called M int j = 5; //index into the array int y = ...

(Sorry, I'm stupid and uneducated, so this is probably a ridiculous question.) I just started looking at J, and they use the terms "monadic" and "dyadic" for what seems (to me) to be unary and bin...

I know all 3 are related, and I've seen quite a few answers for problems in Project Euler written in J, and a few written K. What I'm wondering is, which would you suggest learning, and where...

I'm currently learning the fascinating J programming language, but one thing I have not been able to figure out is how to filter a list. Suppose I have the arbitrary list 3 2 2 7 7 2 9 and I want ...

I picked up J a few weeks ago, about the same time the CodeGolf.SE beta opened to the public. A recurrent issue (of mine) when using J over there is reformatting input and output to fit the proble...

How do I write this C expression in J? (where x is input integer, and a is temporary variable) ((a= ~x & (~x >> 1)) ^= a ? 0 : (a ^ (a & (a - 1))) | (a ^ (a & (a - 1))) <&lt...

Has an emulation of J style of super condensed tacit programming via verbs, adverbs, forks, etc., ever been attempted via libraries for mainstream functional languages? If so, how successful was t...

I just downloaded the Haskell and J modes off of SourceForge, and I'm having trouble figuring out how to make them interface with emacs 23. Google searches yield detailed instructions for emacs 22,...