Course of Raku / Addendum 🆕 / Working with data / Lists, arrays, and hashes / Exercises / Running totals

Solution: Running totals

Here is a possible solution to the task.

Code

my @numbers = 2, 4, 6, 8;

my $sum = 0;
my @totals = @numbers.map({ $sum += $_ });

say @totals;

🦋 You can find the source code in the file running-totals.raku.

Output

[2 6 12 20]

Comments

1. The block keeps a running $sum in a variable outside the map. Each call adds the current element and returns the new total, so the mapped list is the sequence of partial sums.

2. Raku has this built in. The triangular reduction [\+] keeps every partial sum, so the whole solution is a single expression:

   my @numbers = 2, 4, 6, 8;
   say [\+] @numbers; # (2 6 12 20)

   It returns a Seq, so its gist uses parentheses — (2 6 12 20) — rather than the array’s [2 6 12 20], but the numbers are the same.

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