45 lines
2.0 KiB
Plaintext
45 lines
2.0 KiB
Plaintext
created: 20230316151518640
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modified: 20230327130626715
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tags: [[Filter Run Prefix]]
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title: Interchangeable Filter Run Prefixes
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type: text/vnd.tiddlywiki
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!! Interchangeable Filter Run Prefixes
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In technical / logical terms:
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|!Run |!Equivalent named prefix |!Interpretation |!Output |
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|`[run]` |`:or[run]` |de-duplicated union of sets |... OR run |
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|`+[run]` |`:and[run]` |accumulation of filter steps |... AND run |
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|`-[run]` |`:except[run]` |difference of sets |... AND NOT run |
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|`~[run]` |`:else[run]` |else |... ELSE run |
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|`=[run]` |`:all[run]` |union of sets without de-duplication |... OR run |
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The input of a run is normally a list of all the non-[[shadow|ShadowTiddlers]] tiddler titles in the wiki (in no particular order).<br>But the `+` prefix can change this:
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|Prefix|Input|h
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|`-`, `~`, `=`, `:intersection` or none| <$link to="all Operator">`[all[]]`</$link> tiddler titles, unless otherwise determined by the first [[filter operator|Filter Operators]]|
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|`+`, `:filter`, `:map`, `:reduce`,`:sort` |the filter output of all previous runs so far|
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Precisely because of varying inputs, be aware that both prefixes `-` and `+` do not behave inverse to one another!
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For example, in both of the following, `$:/baz` will only be removed if it actually exists:
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* <$link to="is Operator"> `foo bar $:/baz -[is[system]]`</$link>
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* <$link to="prefix Operator">`foo bar $:/baz -[prefix[$:/]]`</$link>
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To understand why, consider the input for both final runs with their `-` prefix.
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In order to remove `$:/baz` in any case, existing or not, simply use the `+` prefix with [[negated filter operators|Filter Operators]]:
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* <$link to="is Operator">`foo bar $:/baz +[!is[system]]`</$link>
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* <$link to="prefix Operator">`foo bar $:/baz +[!prefix[$:/]]`</$link>
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!! Difference between + and intersection
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For the difference between `+` and `:intersection`, see [[Intersection Filter Run Prefix (Examples)]].
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!! For Developers
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To create a new filter run prefix, create a [[Javascript module|Modules]] with a [[module-type|ModuleType]] of `filterrunprefix`.
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