J Interview Questions Answers

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Professional J Programming Language FAQ Questions and Answers

Welcome to our comprehensive Trivia Quiz and interview preparation guide. Below you will find a curated list of popular Trivia Questions and Answers specifically for J Programming Language. Whether you are preparing for a technical interview or just testing your knowledge, these FAQ Questions will help you succeed.

What is the J programming language?

J is a high-level, array-oriented, functional programming language derived from APL.

Who created J?

J was developed by Kenneth E. Iverson and Roger Hui in the early 1990s.

What is the main purpose of J?

J is designed for mathematical, statistical, and array processing tasks.

What kind of syntax does J use?

J uses a tacit (point-free) and concise syntax without parentheses.

What is an atomic function in J?

Atomic functions (also called primitives) operate on entire arrays without loops.

What is the difference between monadic and dyadic functions in J?

Monadic functions take one argument, dyadic functions take two arguments.

How do you define a variable in J?

x =: 10 assigns the value 10 to x.

What is the meaning of +: 5 in J?

It means 5 + 5, because +: is the double function.

How do you add two numbers in J?

5 + 3 evaluates to 8.

What does */ 1 2 3 return?

It returns 6 (i.e., 1 ? 2 ? 3).

How do you create an array in J?

1 2 3 4 creates a vector (1D array).

What does i. 5 return?

It returns 0 1 2 3 4, an index vector.

How do you reshape an array in J?

2 3 $ 1 2 3 4 5 6 creates a 2?3 matrix.

What is the role of $ in J?

$ is the reshape operator.

What does , do in J?

, is the ravel (flatten) operator, which converts multi-dimensional arrays into a single vector.

What does +/ 1 2 3 4 return?

It returns 10 (1+2+3+4).

What is the difference between +/ and * in J?

+/ sums elements, * is the multiplication operator.

How do you find the mean of a list in J?

(+/ % #) 1 2 3 4 gives the mean 2.5.

How do you extract the first element of a list?

0 { 1 2 3 4 returns 1.

What does >: 5 return?

It returns 6, as >: means increment by 1.

What does 5 < 3 return?

It returns 0 (false).

What does 5 > 3 return?

It returns 1 (true).

What is a gerund in J?

A gerund is a list of functions used for advanced control structures.

How do you apply a function to each element of a list?

Using f"0, e.g., *:"0 1 2 3 squares each element.

How do you perform element-wise multiplication?

1 2 3 * 4 5 6 returns 4 10 18.

How do you find the length of a list in J?

# 1 2 3 4 returns 4.

What does i. 3 3 return?

A 3?3 matrix of indices: 0 1 2 / 3 4 5 / 6 7 8.

What does `

. 1 2 3 4` do?

How do you concatenate two lists in J?

(1 2 3), (4 5 6) results in 1 2 3 4 5 6.

What does *. 1 0 1 0 return?

It returns 1 0 1 0 (boolean multiplication).

How do you apply a function over columns of a matrix?

+/ "1 matrix sums each column.

How do you define a function in J?

double =: *:, so double 5 returns 25.

What does ? 5 return?

A random integer between 0 and 4.

What is the role of /. in J?

It is the partition operator for grouping elements.

How do you count unique elements in J?

# ~. 1 2 2 3 3 3 4 returns 4.

How do you generate a range in J?

i. 10 generates 0 1 2 ... 9.

How do you check if a number is in a list?

3 e. 1 2 3 4 returns 1 (true).

What does ; do in J?

It flattens a nested list.

How do you find the maximum in a list?

>./ 1 5 2 4 returns 5.

What does <. do in J?

It returns the floor of a number.

What does >. do in J?

It returns the ceiling of a number.

How do you create a 2x2 identity matrix?

2 2 $ 1 0 0 1.

How do you find the absolute difference between numbers?

What does 1 0 1 0 # 5 6 7 8 return?

It selects values where the mask is 1, so it returns 5 7.

What does ^. 2 return?

It returns the natural logarithm of 2.

What does *: 3 do?

It squares 3, returning 9.

How do you find the dot product of two vectors?

1 2 3 +/ . * 4 5 6 returns 32.

What is an adverb in J?

An adverb modifies the behavior of a verb, e.g., / makes + become summation.

What is a conjunction in J?

A conjunction combines verbs, e.g., +/ (sum reduction).

How do you create a custom operator in J?

Using dyadic defn: F =: dyad : 0