Partition

The collection split into consecutive, non-overlapping chunks of length n.

✓ checked against that system · ! checked, with disagreements (hover a chip)WikipediaPartition of a set↗MathWorldSetPartition↗WikidataQ381060↗Britannicatopic/partition-of-a-set↗Wolfram LanguagePartition✓↗

Partition(collection, n)the collection split into non-overlapping chunks of length n.

Partition(collection, n, d)overlapping sliding windows of length n, offset by d between windows.

Partition(collection, {n1, n2, …}, d)a rank-k array cut into rectangular blocks of shape $\{n_1, n_2, …\}$, offset by d (shared, or one per dimension) between windows — a matrix into overlapping 2×2 blocks, say.

Partition(collection, n, d, {kL, kR}, pad?)sliding windows whose overhang past either end of the collection wraps around cyclically, or — with a trailing pad — is filled with pad instead.

Typed signatures

Type	Package	Applies
(any, any, any?, any?, any?) -> any	combinatoricsreplaces compute-engine	always
(indexed_collection<T>, ((T) any -> boolean) | integer, integer?) -> list<list<T>> where T: any	compute-engine	always

Domain: Collections

Details

• Flatten undoes Partition: chunking and re-flattening recovers the original list — when the length divides evenly.
• With $d < n$, windows overlap; the two-argument form is equivalent to $d = n$, giving non-overlapping chunks.
• A ragged remainder, shorter than $n$, is dropped rather than kept as a partial chunk.
• A list of sizes generalizes chunking to a rank-k array: each dimension gets its own window size (and, optionally, its own offset).
• The overhang pair $\{k_L, k_R\}$ pins where the first window starts and the last one ends, each counted from the near end of the collection — 1-based, negative counting from the far end of the WINDOW instead. Without a padding element, an overhang past either end wraps around cyclically.

Examples

2 more kept as data, checked against the oracles

Basic #

live ↗

In$\mathrm{Partition}(\bigl\lbrack1, 2, 3, 4, 5, 6\bigr\rbrack, 2)$Out$\bigl\lbrack\bigl\lbrack1, 2\bigr\rbrack, \bigl\lbrack3, 4\bigr\rbrack, \bigl\lbrack5, 6\bigr\rbrack\bigr\rbrack$

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f\bigr\rbrack, 2)$Out$\bigl\lbrack\bigl\lbrack a, b\bigr\rbrack, \bigl\lbrack c, d\bigr\rbrack, \bigl\lbrack k, f\bigr\rbrack\bigr\rbrack$

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f\bigr\rbrack, 3, 1)$Out$\bigl\lbrack\bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack b, c, d\bigr\rbrack, \bigl\lbrack c, d, k\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack\bigr\rbrack$

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f\bigr\rbrack, \mathrm{UpTo}(4))$Out$\bigl\lbrack\bigl\lbrack a, b, c, d\bigr\rbrack, \bigl\lbrack k, f\bigr\rbrack\bigr\rbrack$

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f\bigr\rbrack, 5, 1, \bigl\lbrack1, 1\bigr\rbrack)$Out$\bigl\lbrack\bigl\lbrack a, b, c, d, k\bigr\rbrack, \bigl\lbrack b, c, d, k, f\bigr\rbrack, \bigl\lbrack c, d, k, f, a\bigr\rbrack, \bigl\lbrack d, k, f, a, b\bigr\rbrack, \bigl\lbrack k, f, a, b, c\bigr\rbrack, \bigl\lbrack f, a, b, c, d\bigr\rbrack\bigr\rbrack$

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f\bigr\rbrack, 5, 1, \bigl\lbrack-1, 1\bigr\rbrack)$Out$\bigl\lbrack\bigl\lbrack c, d, k, f, a\bigr\rbrack, \bigl\lbrack d, k, f, a, b\bigr\rbrack, \bigl\lbrack k, f, a, b, c\bigr\rbrack, \bigl\lbrack f, a, b, c, d\bigr\rbrack, \bigl\lbrack a, b, c, d, k\bigr\rbrack, \bigl\lbrack b, c, d, k, f\bigr\rbrack, \bigl\lbrack c, d, k, f, a\bigr\rbrack, \bigl\lbrack d, k, f, a, b\bigr\rbrack, \bigl\lbrack k, f, a, b, c\bigr\rbrack, \bigl\lbrack f, a, b, c, d\bigr\rbrack\bigr\rbrack$

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f\bigr\rbrack, 3, 1, \bigl\lbrack1, 1\bigr\rbrack, \mathrm{pad})$Out$\bigl\lbrack\bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack b, c, d\bigr\rbrack, \bigl\lbrack c, d, k\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack, \bigl\lbrack k, f, \mathrm{pad}\bigr\rbrack, \bigl\lbrack f, \mathrm{pad}, \mathrm{pad}\bigr\rbrack\bigr\rbrack$

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f\bigr\rbrack, 3, 1, \bigl\lbrack-1, -1\bigr\rbrack, \mathrm{pad})$Out$\bigl\lbrack\bigl\lbrack\mathrm{pad}, \mathrm{pad}, a\bigr\rbrack, \bigl\lbrack\mathrm{pad}, a, b\bigr\rbrack, \bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack b, c, d\bigr\rbrack, \bigl\lbrack c, d, k\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack\bigr\rbrack$

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f\bigr\rbrack, 3, 1, \bigl\lbrack-1, 1\bigr\rbrack, \mathrm{pad})$Out$\bigl\lbrack\bigl\lbrack\mathrm{pad}, \mathrm{pad}, a\bigr\rbrack, \bigl\lbrack\mathrm{pad}, a, b\bigr\rbrack, \bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack b, c, d\bigr\rbrack, \bigl\lbrack c, d, k\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack, \bigl\lbrack k, f, \mathrm{pad}\bigr\rbrack, \bigl\lbrack f, \mathrm{pad}, \mathrm{pad}\bigr\rbrack\bigr\rbrack$

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f\bigr\rbrack, 4, 1, \bigl\lbrack-1, 1\bigr\rbrack, \bigl\lbrack\mathrm{pad}, \mathrm{dap}\bigr\rbrack)$Out$\bigl\lbrack\bigl\lbrack\mathrm{dap}, \mathrm{pad}, \mathrm{dap}, a\bigr\rbrack, \bigl\lbrack\mathrm{pad}, \mathrm{dap}, a, b\bigr\rbrack, \bigl\lbrack\mathrm{dap}, a, b, c\bigr\rbrack, \bigl\lbrack a, b, c, d\bigr\rbrack, \bigl\lbrack b, c, d, k\bigr\rbrack, \bigl\lbrack c, d, k, f\bigr\rbrack, \bigl\lbrack d, k, f, \mathrm{pad}\bigr\rbrack, \bigl\lbrack k, f, \mathrm{pad}, \mathrm{dap}\bigr\rbrack, \bigl\lbrack f, \mathrm{pad}, \mathrm{dap}, \mathrm{pad}\bigr\rbrack\bigr\rbrack$

Scope #

A third, offset argument produces overlapping sliding windows

live ↗

In$\mathrm{Partition}(\bigl\lbrack1, 2, 3, 4, 5, 6\bigr\rbrack, 3, 1)$Out$\bigl\lbrack\bigl\lbrack1, 2, 3\bigr\rbrack, \bigl\lbrack2, 3, 4\bigr\rbrack, \bigl\lbrack3, 4, 5\bigr\rbrack, \bigl\lbrack4, 5, 6\bigr\rbrack\bigr\rbrack$

Windows of 3 with offset 2 share one element with their neighbour

live ↗

In$\mathrm{Partition}(\bigl\lbrack1, 2, 3, 4, 5, 6, 7\bigr\rbrack, 3, 2)$Out$\bigl\lbrack\bigl\lbrack1, 2, 3\bigr\rbrack, \bigl\lbrack3, 4, 5\bigr\rbrack, \bigl\lbrack5, 6, 7\bigr\rbrack\bigr\rbrack$

An offset larger than the size skips elements between chunks

live ↗

In$\mathrm{Partition}(\bigl\lbrack1, 2, 3, 4, 5, 6, 7\bigr\rbrack, 2, 3)$Out$\bigl\lbrack\bigl\lbrack1, 2\bigr\rbrack, \bigl\lbrack4, 5\bigr\rbrack\bigr\rbrack$

A list of sizes cuts a matrix into overlapping $2 \times 2$ blocks

live ↗

In$\mathrm{Partition}(\bigl\lbrack\bigl\lbrack11, 12, 13\bigr\rbrack, \bigl\lbrack21, 22, 23\bigr\rbrack, \bigl\lbrack31, 32, 33\bigr\rbrack\bigr\rbrack, \bigl\lbrack2, 2\bigr\rbrack, 1)$Out$\bigl\lbrack\bigl\lbrack\bigl\lbrack\bigl\lbrack11, 12\bigr\rbrack, \bigl\lbrack21, 22\bigr\rbrack\bigr\rbrack, \bigl\lbrack\bigl\lbrack12, 13\bigr\rbrack, \bigl\lbrack22, 23\bigr\rbrack\bigr\rbrack\bigr\rbrack, \bigl\lbrack\bigl\lbrack\bigl\lbrack21, 22\bigr\rbrack, \bigl\lbrack31, 32\bigr\rbrack\bigr\rbrack, \bigl\lbrack\bigl\lbrack22, 23\bigr\rbrack, \bigl\lbrack32, 33\bigr\rbrack\bigr\rbrack\bigr\rbrack\bigr\rbrack$

UpTo(4) allows a shorter final chunk, unlike a plain integer count

live ↗

In$\mathrm{Partition}(\bigl\lbrack1, 2, 3, 4, 5, 6\bigr\rbrack, \mathrm{UpTo}(4))$Out$\bigl\lbrack\bigl\lbrack1, 2, 3, 4\bigr\rbrack, \bigl\lbrack5, 6\bigr\rbrack\bigr\rbrack$

Overhangs $\{1, 1\}$ wrap cyclically until the last window starts at the last element

live ↗

In$\mathrm{Partition}(\bigl\lbrack1, 2, 3, 4, 5, 6\bigr\rbrack, 5, 1, \bigl\lbrack1, 1\bigr\rbrack)$Out$\bigl\lbrack\bigl\lbrack1, 2, 3, 4, 5\bigr\rbrack, \bigl\lbrack2, 3, 4, 5, 6\bigr\rbrack, \bigl\lbrack3, 4, 5, 6, 1\bigr\rbrack, \bigl\lbrack4, 5, 6, 1, 2\bigr\rbrack, \bigl\lbrack5, 6, 1, 2, 3\bigr\rbrack, \bigl\lbrack6, 1, 2, 3, 4\bigr\rbrack\bigr\rbrack$

Overhangs $\{-1, 1\}$: the first window ends at the first element, the last starts at the last

live ↗

In$\mathrm{Partition}(\bigl\lbrack1, 2, 3, 4, 5, 6\bigr\rbrack, 5, 1, \bigl\lbrack-1, 1\bigr\rbrack)$Out$\bigl\lbrack\bigl\lbrack3, 4, 5, 6, 1\bigr\rbrack, \bigl\lbrack4, 5, 6, 1, 2\bigr\rbrack, \bigl\lbrack5, 6, 1, 2, 3\bigr\rbrack, \bigl\lbrack6, 1, 2, 3, 4\bigr\rbrack, \bigl\lbrack1, 2, 3, 4, 5\bigr\rbrack, \bigl\lbrack2, 3, 4, 5, 6\bigr\rbrack, \bigl\lbrack3, 4, 5, 6, 1\bigr\rbrack, \bigl\lbrack4, 5, 6, 1, 2\bigr\rbrack, \bigl\lbrack5, 6, 1, 2, 3\bigr\rbrack, \bigl\lbrack6, 1, 2, 3, 4\bigr\rbrack\bigr\rbrack$

A padding element fills the overhang instead of wrapping around

live ↗

In$\mathrm{Partition}(\bigl\lbrack1, 2, 3, 4, 5, 6\bigr\rbrack, 3, 1, \bigl\lbrack1, 1\bigr\rbrack, x)$Out$\bigl\lbrack\bigl\lbrack1, 2, 3\bigr\rbrack, \bigl\lbrack2, 3, 4\bigr\rbrack, \bigl\lbrack3, 4, 5\bigr\rbrack, \bigl\lbrack4, 5, 6\bigr\rbrack, \bigl\lbrack5, 6, x\bigr\rbrack, \bigl\lbrack6, x, x\bigr\rbrack\bigr\rbrack$

Padding on the left, with overhangs $\{-1, -1\}$

live ↗

In$\mathrm{Partition}(\bigl\lbrack1, 2, 3, 4, 5, 6\bigr\rbrack, 3, 1, \bigl\lbrack-1, -1\bigr\rbrack, x)$Out$\bigl\lbrack\bigl\lbrack x, x, 1\bigr\rbrack, \bigl\lbrack x, 1, 2\bigr\rbrack, \bigl\lbrack1, 2, 3\bigr\rbrack, \bigl\lbrack2, 3, 4\bigr\rbrack, \bigl\lbrack3, 4, 5\bigr\rbrack, \bigl\lbrack4, 5, 6\bigr\rbrack\bigr\rbrack$

Padding on both sides, with overhangs $\{-1, 1\}$

live ↗

In$\mathrm{Partition}(\bigl\lbrack1, 2, 3, 4, 5, 6\bigr\rbrack, 3, 1, \bigl\lbrack-1, 1\bigr\rbrack, x)$Out$\bigl\lbrack\bigl\lbrack x, x, 1\bigr\rbrack, \bigl\lbrack x, 1, 2\bigr\rbrack, \bigl\lbrack1, 2, 3\bigr\rbrack, \bigl\lbrack2, 3, 4\bigr\rbrack, \bigl\lbrack3, 4, 5\bigr\rbrack, \bigl\lbrack4, 5, 6\bigr\rbrack, \bigl\lbrack5, 6, x\bigr\rbrack, \bigl\lbrack6, x, x\bigr\rbrack\bigr\rbrack$

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 3)$Out$\bigl\lbrack\bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack\bigr\rbrack$

Overlapping windows of three, sliding by one; the short remainder is dropped

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 3, 1)$Out$\bigl\lbrack\bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack b, c, d\bigr\rbrack, \bigl\lbrack c, d, k\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack, \bigl\lbrack k, f, g\bigr\rbrack\bigr\rbrack$

UpTo keeps the final short block instead of dropping it

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, \mathrm{UpTo}(3))$Out$\bigl\lbrack\bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack, \bigl\lbrack g\bigr\rbrack\bigr\rbrack$

An overhang of one wraps around cyclically to fill the last block

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 3, 3, 1)$Out$\bigl\lbrack\bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack, \bigl\lbrack g, a, b\bigr\rbrack\bigr\rbrack$

A single padding element fills the overhang instead of wrapping

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 3, 3, 1, x)$Out$\bigl\lbrack\bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack, \bigl\lbrack g, x, x\bigr\rbrack\bigr\rbrack$

A padding list is aligned with the positions, so the last block ends in $y, z$

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 3, 3, 1, \bigl\lbrack x, y, z\bigr\rbrack)$Out$\bigl\lbrack\bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack, \bigl\lbrack g, y, z\bigr\rbrack\bigr\rbrack$

An empty padding list gives a short final block

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 3, 3, 1, \bigl\lbrack\bigr\rbrack)$Out$\bigl\lbrack\bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack, \bigl\lbrack g\bigr\rbrack\bigr\rbrack$

A negative overhang puts the short block at the front

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 3, 3, -1, \bigl\lbrack\bigr\rbrack)$Out$\bigl\lbrack\bigl\lbrack a\bigr\rbrack, \bigl\lbrack b, c, d\bigr\rbrack, \bigl\lbrack k, f, g\bigr\rbrack\bigr\rbrack$

Overhang at the end pads the windows that run off the list

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 3, 1, 1, x)$Out$\bigl\lbrack\bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack b, c, d\bigr\rbrack, \bigl\lbrack c, d, k\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack, \bigl\lbrack k, f, g\bigr\rbrack, \bigl\lbrack f, g, x\bigr\rbrack, \bigl\lbrack g, x, x\bigr\rbrack\bigr\rbrack$

Overhang at the start pads windows that begin before the list

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 3, 1, -1, x)$Out$\bigl\lbrack\bigl\lbrack x, x, a\bigr\rbrack, \bigl\lbrack x, a, b\bigr\rbrack, \bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack b, c, d\bigr\rbrack, \bigl\lbrack c, d, k\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack, \bigl\lbrack k, f, g\bigr\rbrack\bigr\rbrack$

Overhang allowed at both ends gives every window touching the list

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 3, 1, \bigl\lbrack-1, 1\bigr\rbrack, x)$Out$\bigl\lbrack\bigl\lbrack x, x, a\bigr\rbrack, \bigl\lbrack x, a, b\bigr\rbrack, \bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack b, c, d\bigr\rbrack, \bigl\lbrack c, d, k\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack, \bigl\lbrack k, f, g\bigr\rbrack, \bigl\lbrack f, g, x\bigr\rbrack, \bigl\lbrack g, x, x\bigr\rbrack\bigr\rbrack$

Limits $[1,-1]$ allow no overhang, matching the plain windows

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 3, 1, \bigl\lbrack1, -1\bigr\rbrack, x)$Out$\bigl\lbrack\bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack b, c, d\bigr\rbrack, \bigl\lbrack c, d, k\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack, \bigl\lbrack k, f, g\bigr\rbrack\bigr\rbrack$

Asymmetric limits: one pad at the front, two at the back

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 3, 1, \bigl\lbrack2, 1\bigr\rbrack, x)$Out$\bigl\lbrack\bigl\lbrack x, a, b\bigr\rbrack, \bigl\lbrack a, b, c\bigr\rbrack, \bigl\lbrack b, c, d\bigr\rbrack, \bigl\lbrack c, d, k\bigr\rbrack, \bigl\lbrack d, k, f\bigr\rbrack, \bigl\lbrack k, f, g\bigr\rbrack, \bigl\lbrack f, g, x\bigr\rbrack, \bigl\lbrack g, x, x\bigr\rbrack\bigr\rbrack$

Cyclic padding $x, y$ fills both overhangs, aligned to the list

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 4, 1, \bigl\lbrack-1, 1\bigr\rbrack, \bigl\lbrack x, y\bigr\rbrack)$Out$\bigl\lbrack\bigl\lbrack y, x, y, a\bigr\rbrack, \bigl\lbrack x, y, a, b\bigr\rbrack, \bigl\lbrack y, a, b, c\bigr\rbrack, \bigl\lbrack a, b, c, d\bigr\rbrack, \bigl\lbrack b, c, d, k\bigr\rbrack, \bigl\lbrack c, d, k, f\bigr\rbrack, \bigl\lbrack d, k, f, g\bigr\rbrack, \bigl\lbrack k, f, g, y\bigr\rbrack, \bigl\lbrack f, g, y, x\bigr\rbrack, \bigl\lbrack g, y, x, y\bigr\rbrack\bigr\rbrack$

Offset exceeding the block length skips elements between blocks

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g, h\bigr\rbrack, 2, 3)$Out$\bigl\lbrack\bigl\lbrack a, b\bigr\rbrack, \bigl\lbrack d, k\bigr\rbrack, \bigl\lbrack g, h\bigr\rbrack\bigr\rbrack$

Wide limits pad whole blocks beyond either end of the list

live ↗

In$\mathrm{Partition}(\bigl\lbrack a, b, c, d, k, f, g\bigr\rbrack, 3, 3, \bigl\lbrack5, -5\bigr\rbrack, x)$Out$\bigl\lbrack\bigl\lbrack x, x, x\bigr\rbrack, \bigl\lbrack x, a, b\bigr\rbrack, \bigl\lbrack c, d, k\bigr\rbrack, \bigl\lbrack f, g, x\bigr\rbrack, \bigl\lbrack x, x, x\bigr\rbrack\bigr\rbrack$

Applications #

Reshaping a list of 9 into a $3 \times 3$ matrix

live ↗

In$\mathrm{Partition}(\bigl\lbrack1, 2, 3, 4, 5, 6, 7, 8, 9\bigr\rbrack, 3)$Out$\bigl\lbrack\bigl\lbrack1, 2, 3\bigr\rbrack, \bigl\lbrack4, 5, 6\bigr\rbrack, \bigl\lbrack7, 8, 9\bigr\rbrack\bigr\rbrack$

Possible issues #

$\{1..5\}$ partitioned by 2 drops the ragged remainder $\{5\}$

live ↗

In$\mathrm{Partition}(\bigl\lbrack1, 2, 3, 4, 5\bigr\rbrack, 2)$Out$\bigl\lbrack\bigl\lbrack1, 2\bigr\rbrack, \bigl\lbrack3, 4\bigr\rbrack\bigr\rbrack$

About

Examples	40
Checked against	Wolfram Language 40 agree
Crosswalk	WikipediaMathWorldWikidataBritannicaWolfram Language

See also: Flatten, UpTo