# Category:J

**J**

This

**programming language**may be used to instruct a computer to perform a task.

Official website |
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Execution method: | Interpreted |
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Type safety: | Safe |

Type strength: | Strong |

Type checking: | Dynamic |

Lang tag(s): | j |

See Also: |

## the J language

J is a notational programming language designed for interactive use.

It is an array language; data is universally structured as rectangular arrays.

It is a functional language; creation and composition of functions is emphasized.

Object-module and imperative techniques are supported, but not required.

The J programming language was designed and developed by Ken Iverson and Roger Hui. It is a closely related successor to APL, also by Iverson which itself was a successor to the notation Ken Iverson used to teach his classes about computers in the 1950s.

## Reading J

J is meant to be read with the aid of a computer. J sentences are single lines and trying variations and simplifications of an expression is common practice. The first step in understanding any J sentence is to understand the data you started with and the data which resulted. When learning how a J sentence works, you can also try simpler sentences which the same data or perhaps related data.

Unless you attend an institution which has made a J interpreter available to you through your web browser, if you want to see how J works you should probably install a copy of J -- or you can try one of the "try me" links, below. If you want to understand how to experiment with alternative expressions you should probably study some of its documentation.

For example, the phrase `(+/ % #)`

finds the average of a list of numbers.

<lang J> (+/ % #) 1 2 3 2</lang>

To understand how this works, you might try working with simpler sentences and their variations.

<lang J> +/ 1 2 3 6

+/4 5 6

15

# 1 2 3

3

# 2 3 4

3

6 % 3

2

15 % 3

5

(+/ % #) 4 5 6

5</lang>

By themselves, these experiments mean nothing, but if you know that +/ was finding the sum of a list and # was finding the length of a list and that % was dividing the two quantities (and looks almost like one of the classical division symbols) then these experiments might help confirm that you have understood things properly.

## J on RosettaCode

Discussion of the goals of the J community on RC and general guidelines for presenting J solutions takes place at House Style.

## Jers on RosettaCode

- Roger Hui: contributions, J wiki
- Tracy Harms: contributions, J wiki
- Dan Bron: contributions, J wiki
- Arie Groeneveld: contributions
- Raul Miller: contributions, J wiki
- Jose Quintana: contributions, J wiki
- Ric Sherlock: contributions, J wiki
- Avmich: contributions
- VZC: contributions
- Alex 'bathala' Rufon: contributions, J wiki

## try me

Want to try one of those cryptic J lines you see peppered through RC? Try pasting it into the online single-line J interpeter or the web interface for buubot (a Perl IRC bot which has a J evaluation mode: just prefix your line with * jeval*).

If you want to be a bit more interactive, and get some guidance from J gurus, you can join the actual J IRC channel on Freenode, #jsoftware. Buubot and several other J eval bots run there. If you don't have an IRC client you can try freenode's web interface (or just give it a quick spin). More details about the J IRC community is available.

If any of that piques your interest, and you want to explore a little more, you can download J and join the J forums.

## Subcategories

This category has the following 3 subcategories, out of 3 total.

### @

- J examples needing attention (1 P)
- J Implementations (empty)
- J User (39 P)

## Pages in category "J"

The following 200 pages are in this category, out of 1,413 total.

(previous page) (next page)### A

- A* search algorithm
- A+B
- Abbreviations, automatic
- Abbreviations, easy
- Abbreviations, simple
- ABC problem
- ABC words
- Abelian sandpile model
- Abelian sandpile model/Identity
- Abstract type
- Abundant odd numbers
- Abundant, deficient and perfect number classifications
- Accumulator factory
- Achilles numbers
- Ackermann function
- Active object
- Add a variable to a class instance at runtime
- Additive primes
- Address of a variable
- ADFGVX cipher
- AKS test for primes
- Algebraic data types
- Align columns
- Aliquot sequence classifications
- Almkvist-Giullera formula for pi
- Almost prime
- Alternade words
- Amb
- Amicable pairs
- Anadromes
- Anagram generator
- Anagrams
- Anagrams/Deranged anagrams
- Anaprimes
- Angle difference between two bearings
- Angles (geometric), normalization and conversion
- Animate a pendulum
- Animation
- Anonymous recursion
- Anti-primes
- Append a record to the end of a text file
- Append numbers at same position in strings
- Apply a callback to an array
- Apply a digital filter (direct form II transposed)
- Approximate equality
- Apéry's constant
- Arbitrary-precision integers (included)
- Archimedean spiral
- Arena storage pool
- Arithmetic coding/As a generalized change of radix
- Arithmetic derivative
- Arithmetic evaluation
- Arithmetic numbers
- Arithmetic-geometric mean
- Arithmetic-geometric mean/Calculate Pi
- Arithmetic/Complex
- Arithmetic/Integer
- Arithmetic/Rational
- Array concatenation
- Array length
- Arrays
- Ascending primes
- ASCII art diagram converter
- Aspect oriented programming
- Assertions
- Assertions in design by contract
- Associative array/Creation
- Associative array/Iteration
- Associative array/Merging
- Attractive numbers
- Autogram checker
- Average loop length
- Averages/Arithmetic mean
- Averages/Mean angle
- Averages/Mean time of day
- Averages/Median
- Averages/Mode
- Averages/Pythagorean means
- Averages/Root mean square
- Averages/Simple moving average
- AVL tree

### B

- Babbage problem
- Babylonian spiral
- Bacon cipher
- Balanced brackets
- Balanced ternary
- Banker's algorithm
- Barnsley fern
- Base 16 numbers needing a to f
- Base64 decode data
- Base64 encode data
- Bell numbers
- Benford's law
- Bernoulli numbers
- Best shuffle
- Bifid cipher
- Bilinear interpolation
- Bin given limits
- Binary coded decimal
- Binary digits
- Binary search
- Binary strings
- Binomial transform
- Bioinformatics/base count
- Bioinformatics/Sequence mutation
- Biorhythms
- Birthday problem
- Bitmap
- Bitmap/Bresenham's line algorithm
- Bitmap/Bézier curves/Cubic
- Bitmap/Bézier curves/Quadratic
- Bitmap/Flood fill
- Bitmap/Histogram
- Bitmap/Midpoint circle algorithm
- Bitmap/Read a PPM file
- Bitmap/Write a PPM file
- Bitwise IO
- Bitwise operations
- Black box
- Blum integer
- Boolean values
- Boustrophedon transform
- Box the compass
- Boyer-Moore string search
- Brace expansion
- Brazilian numbers
- Break OO privacy
- Brilliant numbers
- Brownian tree
- Bulls and cows
- Bulls and cows/Player
- Burrows–Wheeler transform

### C

- Caesar cipher
- Calculating the value of e
- Calendar
- Calendar - for "REAL" programmers
- Calkin-Wilf sequence
- Call a foreign-language function
- Call a function
- Call a function in a shared library
- Call an object method
- Calmo numbers
- CalmoSoft primes
- Canny edge detector
- Canonicalize CIDR
- Cantor set
- Card shuffles
- Carmichael 3 strong pseudoprimes
- Cartesian product of two or more lists
- Case-sensitivity of identifiers
- Casting out nines
- Catalan numbers
- Catalan numbers/Pascal's triangle
- Catamorphism
- Catmull–Clark subdivision surface
- Change e letters to i in words
- Changeable words
- Chaocipher
- Chaos game
- Character codes
- Chebyshev coefficients
- Check Machin-like formulas
- Check output device is a terminal
- Check that file exists
- Checkpoint synchronization
- Chemical calculator
- Chernick's Carmichael numbers
- Cheryl's birthday
- Chinese remainder theorem
- Chinese zodiac
- Cholesky decomposition
- Chowla numbers
- Church numerals
- Cipolla's algorithm
- Circles of given radius through two points
- Circular primes
- Cistercian numerals
- Classes
- Closest-pair problem
- Closures/Value capture
- Code Golf: Code Golf
- Collect and sort square numbers in ascending order from three lists
- Collections
- Color of a screen pixel
- Color quantization
- Color wheel
- Colorful numbers

- Pages using duplicate arguments in template calls
- Execution method/Interpreted
- Typing/Safe
- Typing/Strong
- Typing/Checking/Dynamic
- Programming Languages
- Programming paradigm/Dynamic
- Programming paradigm/Functional
- Programming paradigm/Imperative
- Programming paradigm/Procedural
- Programming paradigm/Reflective
- Programming paradigm/Tacit