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Question-1. What is the J programming language?
Answer-1: J is a high-level, array-oriented, functional programming language derived from APL.
Question-2. Who created J?
Answer-2: J was developed by Kenneth E. Iverson and Roger Hui in the early 1990s.
Question-3. What is the main purpose of J?
Answer-3: J is designed for mathematical, statistical, and array processing tasks.
Question-4. What kind of syntax does J use?
Answer-4: J uses a tacit (point-free) and concise syntax without parentheses.
Question-5. What is an atomic function in J?
Answer-5: Atomic functions (also called primitives) operate on entire arrays without loops.
Question-6. What is the difference between monadic and dyadic functions in J?
Answer-6: Monadic functions take one argument, dyadic functions take two arguments.
Question-7. How do you define a variable in J?
Answer-7: x =: 10 assigns the value 10 to x.
Question-8. What is the meaning of +: 5 in J?
Answer-8: It means 5 + 5, because +: is the double function.
Question-9. How do you add two numbers in J?
Answer-9: 5 + 3 evaluates to 8.
Question-10. What does */ 1 2 3 return?
Answer-10: It returns 6 (i.e., 1 ? 2 ? 3).
Question-11. How do you create an array in J?
Answer-11: 1 2 3 4 creates a vector (1D array).
Question-12. What does i. 5 return?
Answer-12: It returns 0 1 2 3 4, an index vector.
Question-13. How do you reshape an array in J?
Answer-13: 2 3 $ 1 2 3 4 5 6 creates a 2?3 matrix.
Question-14. What is the role of $ in J?
Answer-14: $ is the reshape operator.
Question-15. What does , do in J?
Answer-15: , is the ravel (flatten) operator, which converts multi-dimensional arrays into a single vector.
Question-16. What does +/ 1 2 3 4 return?
Answer-16: It returns 10 (1+2+3+4).
Question-17. What is the difference between +/ and * in J?
Answer-17: +/ sums elements, * is the multiplication operator.
Question-18. How do you find the mean of a list in J?
Answer-18: (+/ % #) 1 2 3 4 gives the mean 2.5.
Question-19. How do you extract the first element of a list?
Answer-19: 0 { 1 2 3 4 returns 1.
Question-20. What does >: 5 return?
Answer-20: It returns 6, as >: means increment by 1.
Question-21. What does 5 < 3 return?
Answer-21: It returns 0 (false).
Question-22. What does 5 > 3 return?
Answer-22: It returns 1 (true).
Question-23. What is a gerund in J?
Answer-23: A gerund is a list of functions used for advanced control structures.
Question-24. How do you apply a function to each element of a list?
Answer-24: Using f"0, e.g., *:"0 1 2 3 squares each element.
Question-25. How do you perform element-wise multiplication?
Answer-25: 1 2 3 * 4 5 6 returns 4 10 18.
Question-26. How do you find the length of a list in J?
Answer-26: # 1 2 3 4 returns 4.
Question-27. What does i. 3 3 return?
Answer-27: A 3?3 matrix of indices: 0 1 2 / 3 4 5 / 6 7 8.
Question-28. What does `
Answer-28: . 1 2 3 4` do?
Question-29. How do you concatenate two lists in J?
Answer-29: (1 2 3), (4 5 6) results in 1 2 3 4 5 6.
Question-30. What does *. 1 0 1 0 return?
Answer-30: It returns 1 0 1 0 (boolean multiplication).
Question-31. How do you apply a function over columns of a matrix?
Answer-31: +/ "1 matrix sums each column.
Question-32. How do you define a function in J?
Answer-32: double =: *:, so double 5 returns 25.
Question-33. What does ? 5 return?
Answer-33: A random integer between 0 and 4.
Question-34. What is the role of /. in J?
Answer-34: It is the partition operator for grouping elements.
Question-35. How do you count unique elements in J?
Answer-35: # ~. 1 2 2 3 3 3 4 returns 4.
Question-36. How do you generate a range in J?
Answer-36: i. 10 generates 0 1 2 ... 9.
Question-37. How do you check if a number is in a list?
Answer-37: 3 e. 1 2 3 4 returns 1 (true).
Question-38. What does ; do in J?
Answer-38: It flattens a nested list.
Question-39. How do you find the maximum in a list?
Answer-39: >./ 1 5 2 4 returns 5.
Question-40. What does <. do in J?
Answer-40: It returns the floor of a number.
Question-41. What does >. do in J?
Answer-41: It returns the ceiling of a number.
Question-42. How do you create a 2x2 identity matrix?
Answer-42: 2 2 $ 1 0 0 1.
Question-43. How do you find the absolute difference between numbers?
Answer-43: `
Question-44. What does 1 0 1 0 # 5 6 7 8 return?
Answer-44: It selects values where the mask is 1, so it returns 5 7.
Question-45. What does ^. 2 return?
Answer-45: It returns the natural logarithm of 2.
Question-46. What does *: 3 do?
Answer-46: It squares 3, returning 9.
Question-47. How do you find the dot product of two vectors?
Answer-47: 1 2 3 +/ . * 4 5 6 returns 32.
Question-48. What is an adverb in J?
Answer-48: An adverb modifies the behavior of a verb, e.g., / makes + become summation.
Question-49. What is a conjunction in J?
Answer-49: A conjunction combines verbs, e.g., +/ (sum reduction).
Question-50. How do you create a custom operator in J?
Answer-50: Using dyadic defn: F =: dyad : 0
Frequently Asked Question and Answer on J Programming Language
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