$ y (Shape Of)
Returns the shape of the noun y .
The shape of a given noun is...
empty (i.0) for an atom (eg the single letter 'a')
- the number of atoms for a vector (eg a list of numbers)
0 for the empty vector
(3 2) for a 3-by-2 matrix
$ y=: 'a' $ $ y 0 (i.0) -: $ y=: 'a' 1 $ y=: 'abcdefghijkl' 12 ] y=: 'abc' ,: 'def' abc def $ y 2 3
Warning Shape Of ($) behaves differently to Tally (#) (which counts the items in a list).
($ ; #) y=: '' +-+-+ |0|0| +-+-+ ($ ; #) y=: 'a' ++-+ ||1| ++-+ ($ ; #) y=: ,'a' +-+-+ |1|1| +-+-+ ($ ; #) y=: 'abc' +-+-+ |3|3| +-+-+
Common uses
1. To verify if a noun is empty, an atom, or a list.
$ y=: '' 0 $ y=: 'a' $ y=: ,'a' 1 $ y=: ,'abc' 3
2. To check that two matrices have the same number of entries in the same arrangement.
Several primitive dyadic verbs are shape-dependent and give an error if x and y are incompatible.
] y=: 2 3 $ 'abcdef' abc def ] x=: 4 5 $ 'ABCDEF' ABCDE FABCD EFABC DEFAB $ x,y 6 5 $ x,:y 2 4 5 $ x,.y |length error | $x ,.y $ x,.x 4 10
See Also
Tally (#)
x $ y (Shape)
Changes the Shape Of ($) (or re-shapes) the array y to (a vector derived from) x.
$ y=: 'abcdefghijkl' 12 ] z=: 2 2 $ y ab cd $ z 2 2
Warning the resulting Shape Of z ($z -- where z=:x$y)) is not necessarily x unless the items of y are atoms!
y=: 'abcdefghijkl' $ z=: 2 2 $ y 2 2 y=: 3 4$'abcdefghijkl' $ z=: 2 2 $ y 2 2 4
Common uses
1. To create a matrix from a unidimensional list.
2. To change the arrangement of entries in a matrix.
See Also