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https://github.com/Jermolene/TiddlyWiki5
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f60d0ef109
Fixes #5246. Now the reduce operator and :reduce filter run prefix will both return empty output when their input is empty, so that both can be chained together with the else operator or :else prefix.
39 lines
1.7 KiB
Plaintext
39 lines
1.7 KiB
Plaintext
created: 20201004154413968
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modified: 20201204131137081
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tags: [[Operator Examples]] [[reduce Operator]]
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title: reduce Operator (Examples)
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type: text/vnd.tiddlywiki
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\define add-price() [get[price]multiply{!!quantity}add<accumulator>]
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\define num-items() [get[quantity]add<accumulator>]
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\define join-with-commas() [<index>compare:number:gt[0]then<accumulator>addsuffix[, ]addsuffix<currentTiddler>else<currentTiddler>]
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\define multiply-input() [multiply<accumulator>]
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\define display-variable(name)
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''<$text text=<<__name__>>/>'': <code><$text text={{{ [<__name__>getvariable[]] }}}/></code>
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\end
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These examples use the following predefined variables:
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* <<display-variable add-price>>
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* <<display-variable num-items>>
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* <<display-variable join-with-commas>>
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* <<display-variable multiply-input>>
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They also use the following data tiddlers:
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<ul>
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<$list filter="[tag[shopping]!has[draft.of]]">
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<li>
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''<$link><$text text=<<currentTiddler>>/></$link>'' quantity: <$text text={{!!quantity}}/>, price: <$text text={{!!price}}/>
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</li>
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</$list>
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</ul>
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<<.operator-example 1 "[tag[shopping]reduce<num-items>]">>
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<<.operator-example 2 "[tag[shopping]reduce<add-price>]">>
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<<.operator-example 3 "[tag[shopping]reduce<join-with-commas>]" "Uses `<index>` to act differently on the first item than the rest">>
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<<.operator-example 4 "[tag[non-existent]reduce<add-price>]" "Empty input produces empty output">>
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<<.operator-example 5 "[tag[non-existent]reduce<add-price>else[0]]" "Use `else` to ensure output if input was empty">>
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<<.operator-example 6 "=1 =2 =3 +[reduce<multiply-input>]" "Empty initial value is treated as 0 by mathematical operators">>
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<<.operator-example 7 "=1 =2 =3 +[reduce<multiply-input>,[1]]" "Setting initial value is sometimes necessary for correct results">>
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