The ravel function `,`

Ravel is a monadic function

Ravel (a reverse-coinage from unravel) turns an object of arbitrary shape back into a vector.

A ← 2 2 ⍴ 1 22 333 4444
, A

Gives a vector not a matrix:

1 22 333 4444

If applied to a scalar , converts it to a vector of length 1

A ← , 1
⍴ A

gives

Partial ravelling

If specified with integer indices ravel can also operate partially on shapes by ravelling axes using the axis notation. The following command will turn the three dimensional shape into a two dimensional one

A ← ⍳ 24
B ← 2 3 4 ⍴ A
C ← ,[1 2] B
⍴ C

6 4

The range of results can be extended:

A ← ⍳ 120
B ← 2 3 4 5 ⍴ A
C ← , [2 3 4] B
⍴ C

Results in the final three dimensions being collapsed:

2 60

The first and second axes 2 and 3 have been merged - the size of the array remains unchanged - 60 being 2 times 3 times 4 of course.

Note: at the moment the rank can’t be expressed as a function that returns a vector.

Adding New Dimensions

An additional dimension (with a size of 1 to preserve the no of elements) can be inserted between existing dimensions by using fractional indices:

C ← 2 3 4 ⍴ ⍳24
⍴ ,[1.5] C

Results in a new shape of:

2 1 3 4

Error Messages

Note: Error messages are a bit pish

If the Axis are improperly specified a RANK ERROR will be thrown:

C ← 2 3 4 ⍴ ⍳24
⍴ ,[3 4] C

Will give:

Error
C ← 2 3 4 ⍴ ⍳24
⍴ ,[3 4] C
--^
RANK ERROR [Invalid Axis: [3,4] ] on line 2 at character 3

This is true for float axis specifications also:

C ← 2 3 4 ⍴ ⍳24
⍴ ,[4.5] C