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{{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 [ | {{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 <source lang=apl inline>⎕IO</source>. | 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>. | ||
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{| class="wikitable c" style="margin:1em auto" | {| class="wikitable c" style="margin:1em auto" | ||
! [[Monadic | ! [[Monadic function]]s !! [[Dyadic function]]s !! [[Operator]]s | ||
|- | |- | ||
| [[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> | | [[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> | ||
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=== 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?] | ||