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* Improve Filter Syntax documentaion / navigation * update links and missing diagrams * rename legacy prefix to shortcut prefix * Update editions/tw5.com/tiddlers/filters/Filter Operators.tid Co-authored-by: yaisog <m@rcuswinter.de> * Update editions/tw5.com/tiddlers/filters/syntax/And Filter Run Prefix.tid Co-authored-by: yaisog <m@rcuswinter.de> * Update editions/tw5.com/tiddlers/filters/syntax/Sort Filter Run Prefix.tid Co-authored-by: yaisog <m@rcuswinter.de> * Update editions/tw5.com/tiddlers/filters/syntax/Sort Filter Run Prefix.tid Co-authored-by: yaisog <m@rcuswinter.de> * Update editions/tw5.com/tiddlers/filters/syntax/Sort Filter Run Prefix.tid Co-authored-by: yaisog <m@rcuswinter.de> * Update editions/tw5.com/tiddlers/filters/syntax/Cascade Filter Run Prefix.tid Co-authored-by: yaisog <m@rcuswinter.de> * Update editions/tw5.com/tiddlers/filters/syntax/And Filter Run Prefix.tid Co-authored-by: yaisog <m@rcuswinter.de> * add most changes a suggested by yaisog * fix copy / paste from-version * replace operand with parameter in the docs * fix typo * fix typos and improve railroad diagrams consistency * move "new from version" info for filter run prefixes below the table * fix typo transclusion and substitution * Move Filters tiddler to the top level in the TOC * wip-breadcrumbs * breadcrumbs & breadcrumbsList macro final * remove files that do not belong to this PR * restore release banner * add simple / story mode to breadcrumbs * .breadcrumbs macro update comments * new breadcrumbs CSS, woks with small screens * make CSS configurable using hidden-settings * improve CSS fro small screens * remove the initial: recursiveParentTag macro * improve location info for breadcrumbs nav. add "alt-text" for Edge ::after element * breadcrumbs add mode=field * bc add initial docs * breadcrumbsField will also respect the story ordering * add configurable global filterMode setting * improve arrow CSS for browser zooming * add bc links use bc-caption if caption field is non-empty * breadcrumbs improve comments * breadcrumbs aria-lable uses caption if there is one * breadcrumbs improve documentation * breadcrumbs improve docs for sort param * fix showArrows docs * remove .bc-link aria-label .. it's not needed if caption is resolved properly * use subfilter instead of enlist to evaluate the "excluded" variable. Be consistent with toc-macros * remove breadcrumbs macros - they have their own PR now * resolve conflict * add back doc-macros tiddler * integrate :then filter run prefix * remove .breadcrumbs macros and their config tiddlers * fix typos as requested --------- Co-authored-by: yaisog <m@rcuswinter.de>
53 lines
2.4 KiB
Plaintext
53 lines
2.4 KiB
Plaintext
caption: reduce
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created: 20201004154131193
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modified: 20230321133918020
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op-input: a [[selection of titles|Title Selection]] passed as input to the filter
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op-output: the final result of running the subfilter <<.place S>>
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op-parameter: a [[filter expression|Filter Expression]]. Optional second parameter for initial value for accumulator
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op-parameter-name: S
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op-purpose: apply a subfilter to each input title in turn, accumulating a single value
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tags: [[Filter Operators]]
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title: reduce Operator
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type: text/vnd.tiddlywiki
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<<.from-version "5.1.23">> The <<.op reduce>> operator runs a subfilter for each input title, passing the result of the previous subfilter run as a variable. The initial value of the accumulator can optionally be specified. It returns the result of the final subfilter run.
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The <<.op reduce>> operator is used to flatten a list of items down to a single item by repeatedly applying a formula. A typical use is to add up the values in a given field of a list of tiddlers.
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The following variables are available within the subfilter:
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* ''accumulator'' - the result of the previous subfilter run
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* ''currentTiddler'' - the input title
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* ''..currentTiddler'' - the value of the variable `currentTiddler` outside the subfilter. <<.from-version "5.2.0">>
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* ''index'' - the numeric index of the current list item (with zero being the first item in the list)
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* ''revIndex'' - the reverse numeric index of the current list item (with zero being the last item in the list)
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* ''length'' - the total length of the input list
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If the <<.op reduce>> operator receives no input, its output will be empty. The [[else Operator]] can be useful in such cases.
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<<.tip "Literal filter parameters cannot contain square brackets but you can work around the issue by using a variable:">>
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```
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<$set name="sum-input" value="[add<accumulator>]">
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{{{ =1 =2 =3 +[reduce<sum-input>] }}}
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</$set>
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```
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<<.tip "Compare with the analogous named [[filter run prefix|Filter Expression]] `:reduce`">>
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```
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\define num-items() [get[quantity]add<accumulator>]
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[tag[shopping]reduce<num-items>]
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```
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is equivalent to:
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```
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[tag[shopping]] :reduce[get[quantity]add<accumulator>]
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```
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<$macrocall $name=".tip" _="""If the optional second parameter is not given, the initial accumulator value will be empty. Numerical operators treat empty input as if it was the number 0. See the multiply-input examples for how this can affect the result of <<.op reduce>> in some cases."""/>
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<<.operator-examples "reduce">>
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