Category: Chapter 3. Aggregate Data Types

Generate the numbers of the Pascal triangle and print them. The Pascal triangle is a sequence of rows of integers. It starts with a single 1 on the top row, and each following row has one number more, starting and ending with 1, while all of the other items are the sums of the two … Continue reading “📘 Building the Pascal triangle using Perl 6”

Generate and print the product table for the values from 1 to 10. The task does not say anything about how to format the output. First, let us print the results as a list with one line per one multiplication. In Perl 6, there is a cross operator X, which operates over lists and creates a … Continue reading “📘 Building the product table using Perl 6”

Having a hash, count the number of occurrences of each of its values. For example, a hash is a collection mapping a car’s license plate to the colour of the car or a passport number to the name of the street where the person lives. In the first example, the task is to count how … Continue reading “📘 Counting hash values in Perl 6”

Sort a list of hashes using data in their values. This task is commonly performed to sort items where the sortable parameter is one of the values in the hash, for example, sorting a list of people by age. my @people = (    {        name => ‘Kevin’, age => 20,    },    . . .    {        name => ‘Amanda’, age => 19,    },);@people.sort({    %^a<age> … Continue reading “📘 Sort hashes by parameter using Perl 6”

Take a matrix and print its transposed version. A matrix can be represented by nested arrays or lists. For example, here’s a square 2×2 matrix: my @matrix = [1, 2],             [3, 4]; This is how the transposed matrix should look: [[1, 3],[2, 4]] Actually, the outer pair of square brackets, could be added to the initializer of the @matrix variable. … Continue reading “📘 How to transpose a matrix in Perl 6”

Pass a few scalars to a sub and work with them as with an array inside the sub. The task is to take a few scalar parameters and pass them to a single array in the subroutine.  Here is an example of how to do that, prefixing an array name with a star: sub h($sep, … Continue reading “📘 Variadic parameters in a sub in Perl 6”

Pass data, contained in an array, to a subroutine. In Perl 6, an array can be passed to a subroutine as easily as a scalar. You simply define it in a signature and pass it together with other arguments. my @colours = <red green blue>;sub f(@data, $sep) {    @data.join($sep).say;}f(@colours, ‘, ‘); # Prints: red, green, blue The @colours array … Continue reading “📘 Passing arrays to subroutines in Perl 6”

Check if the given array contains increasing (or decreasing) numbers. Given the list of numbers in an array, the task is to tell if all of them are sorted in ascending or descending order. Take an array: my @data = 3, 7, 19, 20, 34; In Perl 6, reduction operators offer a very expressive and … Continue reading “📘 Increasing sequences in Perl 6”

Find the minimum and the maximum numbers in the given list of integers. Finding the minimum and maximum elements of arrays is extremely easy in Perl 6. For iterable objects, the two methods, min and max, are defined. my @list = 7, 6, 12, 3, 4, 10, 2, 5, 15, 6, 7, 8, 9, 3;say @list.min;say @list.max; For the … Continue reading “📘 Finding minimum and maximum using Perl 6”

Print all unique elements of the given array. In Perl 6, objects of the Array type have the unique method. my @a = 2, 3, 7, 4, 5, 5, 6, 2, 10, 7;say @a.unique; The result of running this program is a sequence containing the unique elements: (2 3 7 4 5 6 10). Notice that the values … Continue reading “📘 Finding unique elements using Perl 6”

Count how many times a particular element appears in the array. Let’s have an array with a list of fruits; some of them are repeated. my @data = <     apple       pear      grape     lemon     peach       apple      banana   grape      pineapple  avocado >; Now, the task is to count how many times the element ‘grape’ appears there. First, extract all the elements to a temporary array … Continue reading “📘 Counting the number of occurrences in array using Perl 6”

Form a new array by picking every second element from the original array. There is an array of numbers, and the task is to pick every second element and put them into a new array. Prepare the test data: my @data = 20..30; Here is a possible solution: my @selected = @data[1, 3 … *];say … Continue reading “📘 Taking every second element using Perl 6”

Find the first odd number in a list of integers. The task is to find the first odd number in a given list of odd and even numbers. A good candidate is the firstroutine, which searches for the leftmost value (see, for example, Task 58, Is an element in a list?). Now, we can pass an anonymous … Continue reading “📘 Finding the first odd number using Perl 6”

Tell if the given value is in the list. There are a few approaches to the problem. The most compact one seems to be the use of the smartmatch ~~ operator in combination with the anyfunction: my @array = (10, 14, 0, 15, 17, 20, 30, 35);my $x = 17;say ‘In the list’ if $x ~~ any … Continue reading “📘 Check if an element is in a list in Perl 6”

Calculate the moving average for the given array of numbers. For each element of an array, the moving average is the average value of the last few items or the few elements around it. This kind of analysis is often used to smooth the curve. Let us first generate some random data—an array of a … Continue reading “📘 Computing the moving average using Perl 6”

Find the average value of the given array of numbers. Calculating the average value of an array has two subtasks—calculate the sum and divide it by the size of the array. So, one of the solutions can look like this: my @data = 7, 11, 34, 50, 200;say sum(@data) / @data; Here, the sum built-in function … Continue reading “📘 Computing the average value of an array using Perl 6”

Find the sum of the elements of an array of integers. There is an array of integers: my @a = (4, 6, 8, 1, 0, 58, 1, 34, 7, 4, 2); There is no need to explicitly iterate over the elements to calculate the sum of its elements. Rather use the reduction operator: say [+] @a; … Continue reading “📘 Sum of the elements of an array using Perl 6”

From the given two arrays, find the elements of the first array which do not appear in the second one. Take two arbitrary arrays of integers: my @a = 2, 5, 7, 8, 10;my @b = 1, 3, 5, 7, 9; The program should print 2, 8, and 10. Here is a possible solution: my … Continue reading “📘 Exclusion of two arrays in Perl 6”

Take two arrays and create a new one whose elements are the sums of the corresponding items of the initial arrays. At first, we assume that the arrays are of the same length. In this case, the easiest way to solve the task is to use a meta-operator: my @a = 10..20;my @b = 30..40;my … Continue reading “📘 Adding up two arrays in Perl 6”

Increment each element in an array. In Perl 6, there is no need to explicitly iterate over an array to apply some operation to each element. Use a hyper-operator: @data>>++; Let us try it on a small array: my @data = 1..10;@data>>++;say @data; # [2 3 4 5 6 7 8 9 10 11] The >>++ operator is … Continue reading “📘 Incrementing array elements in Perl 6”