Prototype: Difference between revisions

The prototype is used when an array is expanded or when empty elements are inserted in some other way. [[Take]] and [[Expand]] on a [[character]] array produce an array with spaces, because <code>' '</code> is the prototype of a character array:

       ¯12 ↑ 'whitespace'

   whitespace

       (5 1 5/1 ¯2 1) \ 'whitespace'

white  space

The [[Rank operator]] combines its left operand's result cells by extending them to a common shape like [[Mix]] does. Numeric vectors of different lengths will be expanded with <code>0</code>, the prototype for a simple numeric array.

       (⍳⍤0) 2 3 4

1 2 0 0

1 2 3 0

1 2 3 4

{{Works in|[[Dyalog APL]]}}

An array's prototype is based on its first element, so the array <code>a</code> below has a simple numeric prototype, as does any prefix of <code>a</code>. This property even applies to empty arrays: the expression <code>0 ↑ a</code> results in an empty array with the same prototype as <code>a</code>.  

       ⊢a ← 5 'c' ¯2

5 c ¯2

       4 ↑ 0 ↑ a

0 0 0 0

{{Works in|[[Dyalog APL]]}}

The prototype of an array may be nested. Here, we inspect the prototype of an array containing both character and numeric data. In the prototype, all characters are converted to spaces and all numbers to zeros. Thus the prototype retains type and structure information but not specific values.

       ⊢x ← ⊂'de'(3 4 5)  ⍝ A complicated scalar array

┌──────────┐

│  │0 0 0│

└──┴─────┘

{{Works in|[[Dyalog APL]]}}