Ravel with Axes R←,[K]Y

Y may be any array.

K is either:

A simple fractional scalar adjacent to an axis of Y, or
A simple integer scalar or vector of axes of Y, or
An empty vector

Ravel with axis can be used with selective specification.

R depends on the case of K above.

If K is a fraction, the result R is an array of the same shape as Y, but with a new axis of length 1 inserted at the Kth position.

      ⍴⍴R ←→ 1+⍴⍴Y
      ⍴R  ←→ (1,⍴Y)[⍋K,⍳⍴⍴Y]

Examples

      ,[0.5]'ABC'
ABC
      ⍴,[0.5]'ABC'
1 3
      ,[1.5]'ABC'
A
B
C
      ⍴,[1.5]'ABC'
3 1

      MAT←3 4⍴⍳12
      ⍴,[0.5]MAT
1 3 4
      ⍴,[1.5]MAT
3 1 4
      ⍴,[2.5]MAT
3 4 1

If K is an integer scalar or vector of axes of Y, then:

K must contain contiguous axes of Y in ascending order
R contains the elements of Y ravelled along the indicated axes

Note that if K is a scalar or single element vector, R ←→ Y.

      ⍴⍴R ←→ 1+(⍴⍴Y)-⍴,K

Examples

      M
 1  2  3  4
 5  6  7  8
 9 10 11 12

13 14 15 16
17 18 19 20
21 22 23 24
      ⍴M
2 3 4

      ,[1 2]M
 1  2  3  4
 5  6  7  8
 9 10 11 12
13 14 15 16
17 18 19 20
21 22 23 24
      ⍴,[1 2]M
6 4

      ,[2 3]M
 1  2  3  4  5  6  7  8  9 10 11 12
13 14 15 16 17 18 19 20 21 22 23 24

      ⍴,[2 3]M
2 12

If K is an empty vector a new last axis of length 1 is created.

      ⍴R ←→ (⍴Y),1

Examples

      Q1←'January' 'February' 'March'
      ]display Q1
┌→─────────────────────────────┐
│ ┌→──────┐ ┌→───────┐ ┌→────┐ │
│ │January│ │February│ │March│ │
│ └───────┘ └────────┘ └─────┘ │
└∊─────────────────────────────┘
      ]display ,[⍳0]Q1
┌→───────────┐
↓ ┌→──────┐  │
│ │January│  │
│ └───────┘  │
│ ┌→───────┐ │
│ │February│ │
│ └────────┘ │
│ ┌→────┐    │
│ │March│    │
│ └─────┘    │
└∊───────────┘