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In the APL [[array model]], an array's ravel is the [[vector]] containing all its [[elements]] in [[ravel order]] | {{Built-in|Ravel|,}} is a [[primitive function]] introduced in [[APL\360]] which returns the ''ravel'' of an array. In the APL [[array model]], an array's ravel is the [[vector]] containing all its [[elements]] in [[ravel order]]. It is equivalent to [[Reshape|reshaping]] an array using its [[bound]] for the new [[shape]]. Reshaping the ravel using the original array's shape restores that array. | ||
In some APLs an [[Function axis|axis]] may be specified for Ravel in order to combine only some [[Axis|axes]] of an array, or insert a length-1 axis. | In some APLs an [[Function axis|axis]] may be specified for Ravel in order to combine only some [[Axis|axes]] of an array, or insert a length-1 axis. | ||
The name "ravel" | The name "ravel" references the process of undoing woven or knitted fabric, thus removing its structure and rendering it linear. | ||
== Examples == | == Examples == | ||
You can use ravel to squash a [[matrix]] down to one dimension. The elements are listed in reading order—left to right, top to bottom. | You can use ravel to squash a [[matrix]] down to one dimension. The elements are listed in reading order—left to right, top to bottom. | ||
<source | <source lang=apl> | ||
⎕←x ← 3 4⍴⍳12 ⍝ A matrix | |||
1 2 3 4 | 1 2 3 4 | ||
5 6 7 8 | 5 6 7 8 | ||
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Ravelling a [[scalar]] yields a [[singleton]] [[vector]]. | Ravelling a [[scalar]] yields a [[singleton]] [[vector]]. | ||
<source | <source lang=apl> | ||
,3 | ,3 | ||
3 | 3 | ||
| Line 32: | Line 32: | ||
[[String]] notation cannot produce a single-character string since it produces a [[scalar]] character instead. Using Ravel on a list of characters in quotes ensures it will be a [[vector]] of characters. | [[String]] notation cannot produce a single-character string since it produces a [[scalar]] character instead. Using Ravel on a list of characters in quotes ensures it will be a [[vector]] of characters. | ||
<source | <source lang=apl> | ||
≢⍴ 'a' ⍝ Scalar character | ≢⍴ 'a' ⍝ Scalar character | ||
0 | 0 | ||
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[[Function axis|Axis specification]] may accept either a [[vector]] of two or more adjacent [[axis]] [[Index|indices]], or a single non-integer value. If multiple axes are given, they are merged into one axis whose length is the product of their lengths. If only one value is given, a new axis of length 1 is inserted in the indicated "gap" between axes. | [[Function axis|Axis specification]] may accept either a [[vector]] of two or more adjacent [[axis]] [[Index|indices]], or a single non-integer value. If multiple axes are given, they are merged into one axis whose length is the product of their lengths. If only one value is given, a new axis of length 1 is inserted in the indicated "gap" between axes. | ||
<source | <source lang=apl> | ||
⍴ ,[2 3] 5 4 3 2⍴0 | ⍴ ,[2 3] 5 4 3 2⍴0 | ||
5 12 2 | 5 12 2 | ||
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== Description == | == Description == | ||
The ravel of an array < | The ravel of an array <source lang=apl inline>A</source> has shape <source lang=apl inline>,×/⍴A</source> and shares elements with <source lang=apl inline>A</source>. Thus Ravel may be modelled as a [[Reshape|reshaping]] function <source lang=apl inline>{(×/⍴⍵)⍴⍵}</source>. The [[element]] with [[index]] [[vector]] <source lang=apl inline>I</source> is moved to index <source lang=apl inline>(⍴A)⊥I</source> in [[index origin]] 0, or <source lang=apl inline>⎕IO+(⍴A)⊥I-⎕IO</source> in arbitrary index origin. | ||
As with any reshaping, the result of Ravel has the same [[prototype]] as the argument. | |||
== History == | == History == | ||
| Line 56: | Line 58: | ||
Ravel was present in the first version of [[APL\360]]<ref>Falkoff, A.D., and K.E. Iverson. [https://www.jsoftware.com/papers/APL360TerminalSystem.htm "The APL\360 Terminal System"]. Research Report RC-1922, IBM, 1967-10-16.</ref> and has been included in every APL since. | Ravel was present in the first version of [[APL\360]]<ref>Falkoff, A.D., and K.E. Iverson. [https://www.jsoftware.com/papers/APL360TerminalSystem.htm "The APL\360 Terminal System"]. Research Report RC-1922, IBM, 1967-10-16.</ref> and has been included in every APL since. | ||
== Documentation == | == External links == | ||
=== Lessons === | |||
* [https://chat.stackexchange.com/transcript/52405?m=41726592#41726592 APL Cultivation] | |||
=== Documentation === | |||
[http://help.dyalog.com/latest/ | * [http://help.dyalog.com/latest/index.htm#Language/Primitive%20Functions/Ravel.htm Dyalog] ([http://help.dyalog.com/latest/index.htm#Language/Primitive%20Functions/Ravel%20with%20Axes.htm with axis]), | ||
* [http://wiki.nars2000.org/index.php/Rho NARS2000] | |||
* [http://microapl.com/apl_help/ch_020_020_480.htm APLX] | |||
[https:// | * [https://www.jsoftware.com/help/dictionary/d320.htm J Dictionary], [https://code.jsoftware.com/wiki/Vocabulary/comma J NuVoc] | ||
== References == | == References == | ||
| Line 70: | Line 78: | ||
<references /> | <references /> | ||
{{APL | {{APL features}} | ||
{{APL built-ins}}[[Category:Primitive functions]] | |||