This problem was inspired by Counting DNA Nucleotides found on the excellent bioinformatics website rosalind.info.

Write a function that:

- takes a right argument that is a character vector or scalar representing a DNA string (whose alphabet contains the symbols 'A', 'C', 'G', and 'T').
- returns a 4-element numeric vector containing the counts of each symbol 'A', 'C', 'G', and 'T' respectively.

**Hint:** The *key* operator f⌸ or the *outer product* operator ∘.g could be helpful.

(your_function) 'AGCTTTTCATTCTGACTGCAACGGGCAATATGTCTCTGTGTGGATTAAAAAAAGAGTGTCTGATAGCAGC' 20 12 17 21 (your_function) '' 0 0 0 0 (your_function) 'G' 0 0 1 0

This problem is inspired by the Counting Point Mutations problem found on the excellent Bioinformatics education website rosalind.info.

Write a function that:

- takes right and left arguments that are character vectors or scalars of equal length – these represent DNA strings.
- returns an integer representing the Hamming distance (the number of differences in corresponding positions) between the arguments.

**Hint:** The *plus* function X+Y could be helpful.

'GAGCCTACTAACGGGAT' (your_function) 'CATCGTAATGACGGCCT' 7 'A' (your_function) 'T' 1 '' (your_function) '' 0 (your_function)⍨ 'CATCGTAATGACGGCCT' 0

Write a function that:

- takes right and left arguments that are arrays of arbitrary rank, depth, and value.
- returns a vector of all elements that appear in either of the two argument arrays but not in both. The order of elements in the result is not significant.

**Hint:** The *without* function X~Y could be helpful.

'DYALOG' (your_function) 'APL' DYOGP 'DYALOG' (your_function) ⊂'APL' ┌─┬─┬─┬─┬─┬─┬───┐ │D│Y│A│L│O│G│APL│ └─┴─┴─┴─┴─┴─┴───┘ (2 2⍴'Hello'(⊂'World')(2 2⍴⍳4)42) (your_function) 42 'Have a nice day' ┌─────┬───────┬───┬───────────────┐ │Hello│┌─────┐│1 2│Have a nice day│ │ ││World││3 4│ │ │ │└─────┘│ │ │ └─────┴───────┴───┴───────────────┘ 1 1 1 (your_function) 2 2 1 1 1 2 2

Write a function that:

- takes a right argument that is a Boolean scalar or vector.
- returns the length of the longest sequence of consecutive 1s.

**Hint:** The *partition* function X⊆fY could be helpful.

(your_function) 1 1 1 0 1 1 0 0 1 1 1 1 0 4 (your_function) ⍬ 0 (your_function) 1 1 (your_function) 0 0 (your_function) 12/0 1 0 1 12

(with apologies to Led Zeppelin)

Write a function that:

- takes a scalar integer argument, n, in the range 0-100.
- returns a character matrix comprised of spaces and ⎕ that resembles an n-level left-to-right ascending stairway.

**Hint:** The *index generator* function ⍳Y could help with solving this
problem.

(your_function) 10 ⎕ ⎕⎕ ⎕⎕⎕ ⎕⎕⎕⎕ ⎕⎕⎕⎕⎕ ⎕⎕⎕⎕⎕⎕ ⎕⎕⎕⎕⎕⎕⎕ ⎕⎕⎕⎕⎕⎕⎕⎕ ⎕⎕⎕⎕⎕⎕⎕⎕⎕ ⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕ (your_function) 0 ⍝ returns a 0×0 matrix

Write a monadic function that:

- takes an argument
*n*that is an integer scalar in the range 0-100. - returns a square matrix "pyramid" with 0⌈¯1+2×n rows and columns of n increasing concentric levels.

By this we mean that the center element of the matrix will be n, surrounded on all sides by n-1.

**Hint:** The functions *minimum* X⌊Y and *reverse* ⌽Y, and the *outer product* operator X∘.gY could be helpful.

(your_function) 3 1 1 1 1 1 1 2 2 2 1 1 2 3 2 1 1 2 2 2 1 1 1 1 1 1 (your_function) 5 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 1 1 2 3 3 3 3 3 2 1 1 2 3 4 4 4 3 2 1 1 2 3 4 5 4 3 2 1 1 2 3 4 4 4 3 2 1 1 2 3 3 3 3 3 2 1 1 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 (your_function) 1 ⍝ should return 1 1⍴1 1 (your_function) 0 ⍝ should return 0 0⍴0

Apologies to the code golfers out there, but this problem has nothing to do with code golf! Instead, it addresses the problem of assigning places in a golf tournament. In regular golf, lower scores place higher – the lowest score places first and the highest score places last.

Write a function that:

- takes a right argument that is a non-decreasing vector or scalar of strictly positive integers, representing a set of scores.
- returns a numeric vector of the place for each score; for duplicate scores, it returns the average of the places they hold.

**Hint:** This problem has several viable approaches including using *key*
f⌸, or *partition* X⊆Y,
or *interval index* X⍸Y.

(your_function) 1 2 3 4 5 1 2 3 4 5 (your_function) 68 71 71 73 1 2.5 2.5 4 (your_function) 67 68 68 69 70 70 70 71 72 1 2.5 2.5 4 6 6 6 8 9 (your_function) 6⍴70 3.5 3.5 3.5 3.5 3.5 3.5 (your_function) ⍬ ⍝ this should return an empty vector (your_function) 67 ⍝ should work with a scalar argument 1

Write a function that:

- takes a right argument that is a non-empty character vector or scalar.
- takes a left argument that is a non-empty character vector or scalar.
- returns a 2-element vector of character vectors in which the right argument is split immediately before the
*first*occurence of*any*element in the left argument. If no left-argument element occurs in the right argument, then the split should happen after the last element of the right argument.

**Hint:** The *take*
X↑Y and *drop*
X↓Y functions, or the *partitioned enclose* function
X⊂Y, could be helpful.

'do' (your_function) 'Hello World' ┌────┬───────┐ │Hell│o World│ └────┴───────┘ 'KEI' (your_function) ⎕A ⍝ ⎕A is the system constant that contains the characters A-Z ┌────┬──────────────────────┐ │ABCD│EFGHIJKLMNOPQRSTUVWXYZ│ └────┴──────────────────────┘ (⌽⎕A) (your_function) ⎕A ┌┬──────────────────────────┐ ││ABCDEFGHIJKLMNOPQRSTUVWXYZ│ └┴──────────────────────────┘ ⎕D (your_function) ⎕A ⍝ ⎕D is the system constant that contains the characters 0-9 ┌──────────────────────────┬┐ │ABCDEFGHIJKLMNOPQRSTUVWXYZ││ └──────────────────────────┴┘ ⎕D (your_function) 'Q' ┌─┬┐ │Q││ └─┴┘ ⎕A (your_function) 'Q' ┌┬─┐ ││Q│ └┴─┘

Write a function that:

- takes a right argument Y that is a numeric scalar or non-empty vector.
- takes a left argument X that represents the number of neighboring elements on either side of each element in Y.
- returns a numeric vector or scalar where each element is the average (mean) of the corresponding element in Y and its X neighbors on either side. If an element has fewer than X neighbors on either side, replicate the first and last values as necessary to make X neighbors.

**Hint:** The *Reduce N-Wise* operator Xf/Y could help with solving this
problem.

0 (your_function) 1 2 3 4 5 6 ⍝ 0 neighbors on each side 1 2 3 4 5 6 1 (your_function) 1 2 3 4 5 6 ⍝ 1 neighbors on each side 1.333333333 2 3 4 5 5.666666667 2 (your_function) 1 2 3 4 5 6 ⍝ 2 neighbors on each side 1.6 2.2 3 4 4.8 5.4 6 (your_function) 1 2 3 4 5 6 2.538461538 2.923076923 3.307692308 3.692307692 4.076923077 4.461538462 10 (your_function) 42 42

Write a function that:

- takes a right argument that is a character vector or scalar representing a valid non-negative integer.
- takes a left argument that is a character scalar "separator" character.
- returns a character vector that is a representation of the right argument formatted such that the separator character is found between trailing groups of 3 digits.

Note that the number of digits in the character representation might exceed the number of digits that can be represented as a 32-bit integer.

**Hint:** The *at* operator @ could be helpful.

',' (your_function)¨'1' '10' '100' '1000' '10000' '100000' '1000000' '10000000' '100000000' '1000000000' '10000000000' ┌─┬──┬───┬─────┬──────┬───────┬─────────┬──────────┬───────────┬─────────────┬──────────────┐ │1│10│100│1,000│10,000│100,000│1,000,000│10,000,000│100,000,000│1,000,000,000│10,000,000,000│ └─┴──┴───┴─────┴──────┴───────┴─────────┴──────────┴───────────┴─────────────┴──────────────┘ '.' (your_function) 60⍴⌽⎕D 987.654.321.098.765.432.109.876.543.210.987.654.321.098.765.432.109.876.543.210 '/' (your_function) ,'9' ⍝ scalars and 1-element character vectors are equivalent 9