120
edits
Index origin: Difference between revisions
Jump to navigation
Jump to search
m
15 revisions imported: Migrate from miraheze
Miraheze>Marshall |
m (15 revisions imported: Migrate from miraheze) |
||
| (8 intermediate revisions by 2 users not shown) | |||
| Line 1: | Line 1: | ||
{{ | {{Built-in|Index origin|⎕IO}} is the number used for the first [[index]] along each [[axis]] of an array. Many APLs allow the user to configure index origin using the [[system variable]] <source lang=apl inline>⎕IO</source>. Even array languages which do not have such a configuration parameter must make a choice of index origin; for example, [[A+]] and [[J]] use a non-configurable index origin of 0. The [[wikipedia:English language|English language]] uses an index origin of one: thus the element with index <source lang=apl inline>⎕IO</source> in APL is referred to in English as the "first" element. | ||
The index origin affects both the handling of index arguments to functions (and other functionality like [[axis specification]]) and their results. For example, [[Iota]] (or "Index Generator") creates results which begin with < | The index origin affects both the handling of index arguments to functions (and other functionality like [[axis specification]]) and their results. For example, [[Iota]] (or "Index Generator") creates results which begin with <source lang=apl inline>⎕IO</source>. | ||
< | <source lang=apl> | ||
⎕IO←0 | ⎕IO←0 | ||
⍳4 | ⍳4 | ||
| Line 9: | Line 9: | ||
⍳4 | ⍳4 | ||
1 2 3 4 | 1 2 3 4 | ||
</ | </source> | ||
Any number could consistently be used for the index origin, but almost all APLs restrict the choice to 0 or 1. [[ngn/apl]] supports < | Any number could consistently be used for the index origin, but almost all APLs restrict the choice to 0 or 1. [[ngn/apl]] supports <source lang=apl inline>⎕IO</source> but only allows it to have the value 0. Attempting to assign an unsupported value to <source lang=apl inline>⎕IO</source> typically results in a [[DOMAIN ERROR]]. | ||
The choice of which numbers are indices is subjective and must be made by the language designer. In some cases there is no clear decision: [[Interval Index]] and [[Occurrence Count]] each have natural definitions that depend on index origin, and natural definitions that do not. | The choice of which numbers are indices is subjective and must be made by the language designer. In some cases there is no clear decision: [[Interval Index]] and [[Occurrence Count]] each have natural definitions that depend on index origin, and natural definitions that do not. | ||
| Line 17: | Line 17: | ||
== Functions which depend on index origin == | == Functions which depend on index origin == | ||
The following functions depend on < | The following functions depend on <source lang=apl inline>⎕IO</source> in at least some APLs. They are listed with the [[glyph]]s used for them in [[Dyalog APL]]. For functions, only the result depends on <source lang=apl inline>⎕IO</source> except where noted with <source lang=apl inline>⍺</source> in which case the left argument does instead. For operators the dependence is noted. | ||
{| class="wikitable c" style="margin:1em auto" | {| class="wikitable c" style="margin:1em auto" | ||
! [[Monadic | ! [[Monadic function]]s !! [[Dyadic function]]s !! [[Operator]]s | ||
|- | |- | ||
| [[Iota]] (< | | [[Iota]] (<source lang=apl inline>⍳</source>) || [[Index-Of]] (<source lang=apl inline>⍳</source>) || [[Key]] (<source lang=apl inline>⌸</source>) argument to <source lang=apl inline>⍺⍺</source> | ||
|- | |- | ||
| [[Roll]] (< | | [[Roll]] (<source lang=apl inline>?</source>) || [[Deal]] (<source lang=apl inline>?</source>) || [[At]] (<source lang=apl inline>@</source>) result of <source lang=apl inline>⍵⍵</source> | ||
|- | |- | ||
| [[Grade]] (< | | [[Grade]] (<source lang=apl inline>⍒⍋</source>) || (<source lang=apl inline>⍒⍋</source>) || | ||
|- | |- | ||
| [[Indices]] (< | | [[Indices]] (<source lang=apl inline>⍸</source>) || [[Interval Index]] (<source lang=apl inline>⍸</source>) || | ||
|- | |- | ||
| || [[Transpose]] (< | | || [[Transpose]] (<source lang=apl inline>⍉</source>) <source lang=apl inline>⍺</source> || | ||
|- | |- | ||
| || [[Pick]] (< | | || [[Pick]] (<source lang=apl inline>⊃</source>) <source lang=apl inline>⍺</source> || | ||
|- | |- | ||
| || [[Squad]] (< | | || [[Squad]] (<source lang=apl inline>⌷</source>) <source lang=apl inline>⍺</source> || | ||
|} | |} | ||
| Line 43: | Line 43: | ||
=== Articles === | === Articles === | ||
* [ | * [[wikipedia:Array_data_type#Index_origin|Wikipedia]] | ||
* [https://www.jsoftware.com/papers/indexorigin.htm Is Index Origin 0 a Hindrance?] | * [https://www.jsoftware.com/papers/indexorigin.htm Is Index Origin 0 a Hindrance?] | ||
| Line 54: | Line 53: | ||
* [https://help.dyalog.com/latest/index.htm#Language/System%20Functions/io.htm Dyalog] | * [https://help.dyalog.com/latest/index.htm#Language/System%20Functions/io.htm Dyalog] | ||
* [http://microapl.com/apl_help/ch_020_070_380.htm APLX] | * [http://microapl.com/apl_help/ch_020_070_380.htm APLX] | ||
{{APL built-ins}} | {{APL built-ins}} | ||