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Shape Of $  _ 1 _ Shape

$ y yields the shape of y as defined in Section II A. For example, the shape of a 2-by-3 matrix is 2 3, and the shape of the scalar 3 is an empty list (whose shape is 0).

The rank of an argument y is #@$ y . For example:
   rank=: #@$
   (rank 3) , (rank ,3)
0 1

   (rank 3 4),(rank i. 2 3 4)
1 3
  The shape of x$y is x,siy where siy is the shape of an item of y; x$y gives a length error if y is empty and x,siy does not contain a zero. For example:
   y=: 3 4$'abcdefghijkl'
   y ; 2 2$ y
+----+----+
|abcd|abcd|
|efgh|efgh|
|ijkl|    |
|    |ijkl|
|    |abcd|
+----+----+
This example shows how the result is formed from the items of y, the last 1-cell (abcd) showing that the selection is cyclic. The fit conjunction ($!.f) provides fill specified by the items of f .
 

Since x $ y uses items from y, it is sometimes useful to ravel the right argument, as in x $ ,y. For example (using the y defined above):
   2 3 $ ,y
abc
def
The fit conjunction is often useful for appending zeros or spaces. For example:
   8 $!.0 (2 3 4)
2 3 4 0 0 0 0 0

   ]z=: 8$!.'*' 'abc'
abc*****
            
   |. z
*****cba

   2 5$!.a: ;: 'zero one two three four five six'
+----+---+---+-----+----+
|zero|one|two|three|four|
+----+---+---+-----+----+
|five|six|   |     |    |
+----+---+---+-----+----+


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