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42 lines
2.8 KiB
Plaintext
42 lines
2.8 KiB
Plaintext
created: 20210618134753828
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modified: 20211125152755859
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tags: [[Filter Syntax]] [[Filter Run Prefix Examples]] [[Map Filter Run Prefix]]
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title: Map Filter Run Prefix (Examples)
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type: text/vnd.tiddlywiki
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Replace the input titles with the caption field if it exists, otherwise preserve the input title:
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<<.operator-example 1 "[tag[Widgets]] :map[get[caption]else{!!title}]">>
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<<.tip "The above example is equivalent to `[tag[Widgets]] :map[{!!caption}!is[blank]else{!!title}]`. Note that referencing a field as a text reference such as `{!!caption}` returns an empty string for a non-existent or empty caption field. Therefore a check for `is[blank]` is needed before the `else` operator">>
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For each title in a shopping list, calculate the total cost of purchasing each item:
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<<.operator-example 2 "[tag[shopping]] :map[get[quantity]else[0]multiply{!!price}]">>
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!! Comparison between `:map` and `:and`/`+` filter run prefixes
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The functionality of the `:map` filter run prefix has some overlap with the `:and` prefix (alias `+`). They will sometimes return the same results as each other. In at least these cases, the results will be different:
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# The `:and` filter run can modify the number of items (either increase or decrease). The `:map` run will never alter the number of items.
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# The number of items in the `:and` filter run will also decrease due to de-duplication. The `:map` run will not de-duplicate.
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# Explicit references to the "currentTiddler" variable will behave differently
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# Implicit references to the "currentTiddler" using TextReference will behave differently.
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| `:map` | `:and` |
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|!results are the same|<|
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|^<<.operator-example 1.1 "[range[5]] :map[add[1]]">>|^<<.operator-example 1.2 "[range[5]] :and[add[1]]">>|
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|^<<.operator-example 2.1 "[range[5]] :map[addsuffix[ hello]]">>|^<<.operator-example 2.2 "[range[5]] :and[addsuffix[ hello]]">>|
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|^<<.operator-example 3.1 "[tag[shopping]] :map[get[quantity]]">>|^<<.operator-example 3.2 "[tag[shopping]] :and[get[quantity]]">>|
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|!decrease in the number of items|<|
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|^<<.operator-example 4.1 "[range[5]] :map[sum[]]">>|^<<.operator-example 4.2 "[range[5]] :and[sum[]]">>|
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|^<<.operator-example 5.1 "[range[5]] :map[join[,]]">>|^<<.operator-example 5.2 "[range[5]] :and[join[,]]">>|
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|!increase in the number of items|<|
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|^<<.operator-example 6.1 "[[1,2,3]] [[4,5]] :map[split[,]]">>|^<<.operator-example 6.2 "[[1,2,3]] [[4,5]] :and[split[,]]">>|
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|!de-duplication|<|
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|^<<.operator-example 7.1 "[range[5]] :map[[hello]]">>|^<<.operator-example 7.2 "[range[5]] :and[[hello]]">>|
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|!currentTiddler|<|
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|^<<.operator-example 8.1 "[tag[shopping]] :map[<currentTiddler>]">>|^<<.operator-example 8.2 "[tag[shopping]] :and[<currentTiddler>]">>|
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|^<<.operator-example 9.1 "[tag[shopping]] :map[{!!quantity}]">>|^<<.operator-example 9.2 "[tag[shopping]] :and[{!!quantity}]">>|
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