Reshaping lists — flat, rotor, scan

Flatten nesting, slide a window, and produce running totals.

These methods change a list's shape rather than its contents: .flat removes nesting, .rotor groups into (possibly overlapping) chunks, and the triangular reduce [\op] produces running results.

flat — remove nesting #

.flat flattens nested lists into one flat sequence, however deep.

say ((1, 2), (3, 4)).flat;
say (1, (2, (3, 4))).flat;

(1 2 3 4)
(1 2 3 4)

rotor — sliding windows #

.rotor(n) makes chunks of n; .rotor(n => -k) overlaps them by k — a sliding window.

say (1..5).rotor(2 => -1);

((1 2) (2 3) (3 4) (4 5))

Triangular reduce — running totals #

[\op] is the scan form of the reduction metaoperator: it keeps every intermediate result, not just the final one.

say [\+] 1, 2, 3, 4;

(1 3 6 10)

Each element is the running sum: 1, 1+2, 1+2+3, 1+2+3+4.

Notes #

• .flat only flattens list structure; a scalar holding a list (an itemised $) stays opaque, which is how nested data is kept intact when you want it.
• .rotor also takes uneven batch sizes and a :partial flag for handling a short final chunk.
• [\*], [\~], and any other associative operator work as scans too — [\~] <a b c> gives (a ab abc).