TiddlyWiki5/editions/tw5.com/tiddlers/widgets/ActionListopsWidget.tid

caption: action-listops
created: 20141025120850184
list: efg hlm pqr
modified: 20151228083329099
myfield: 
revision: 0
tags: ActionWidgets Widgets
title: ActionListopsWidget
type: text/vnd.tiddlywiki

\define .operator-rows(filter)
<$list filter="$filter$"><tr>
<td><$link>{{!!caption}}</$link></td>
<td>{{!!op-purpose}} <$list filter="[all[current]tag[Common Operators]]">{{$:/core/images/done-button}}</$list></td>
<td align="center"><$list filter="[all[current]tag[Negatable Operators]]">`!`</$list></td>
</tr></$list>
\end

\define .group-heading(_)
<tr class="doc-table-subheading"><th colspan="3" align="center">$_$</th></tr>
\end

! Introduction

The ''action-listops'' widget is an [[action widget|ActionWidgets]] that manipulates user lists in any field or data index. ActionWidgets are used within triggering widgets such as the ButtonWidget.

! Content and Attributes

The ''action-listops'' widget is invisible. Any content within it is ignored.

|!Attribute |!Description |
|$tiddler |The title of the tiddler whose lists are to be modified (if not provided defaults to the [[current tiddler|Current Tiddler]] |
|$field |The name of a field to be manipulated as a list (defaults to 'list') |
|$index |Optional index of a property in a [[data tiddler|DataTiddlers]] index to be manipulated as a list |
|$filter |An optional filter expression, the output of which will be saved to the field/index being manipulated |
|$subfilter |An optional subfilter expression, which takes the list being manipulated as input, and saves the modified list back to the field/index being manipulated |
|$tags |An optional subfilter expression, which takes the 'tags' field of the target tiddler as input, and saves the modified list of tags back to the 'tags' field |

! $filter vs. $subfilter

Standalone use of the `$subfilter` attribute can be replaced by using a (more complicated) `$filter` attribute value.

For example, the items "abc" and "123" can be appended to the field `myfield` using the `$subfilter` attribute:

```
<$action-listops $field="myfield" $subfilter="abc 123"/>
```

The same can be achieved using the `$filter` attribute and prepending the [[Filter Run]] `[all[current]get[myfield]enlist-input[]]` to the [[Filter Expression]]:

```
<$action-listops $field="myfield" $filter="[all[current]get[myfield]enlist-input[]] abc 123"/>
```

The short form is more convenient, but the long form is useful for live-debugging complicated `$subfilter` values using the filter tab of [[$:/AdvancedSearch]]. By using [[$:/AdvancedSearch]], the [[Filter Expression]] can be tested before using ''action-listops'' to modify actual tiddler fields. For this use case, the `all[current]` portion of the expression needs to be changed to select the proper test tiddler.

! $tags vs. $field + $subfilter

[[Tagging]] is implemented using a tiddler's 'tags' field, so appending the tags "abc" and "123" using the `$tags` attribute like this:

```
<$action-listops $tags="abc 123"/>
```

is mostly equivalent to using `$subfilter` along with "tags" for the value of `$field`:

```
<$action-listops $field="tags" $subfilter="abc 123"/>
```

! $action-listops widget vs. $action-setfield widget

The ActionSetFieldWidget replaces a field's value using `$field`/`$value` attributes. A single ActionSetFieldWidget can be used to set any number of fields by using attributes not starting with $.

The ActionListopsWidget replaces or modifies a single field's value. The new value is generated using filters.

The following two examples are functionally equivalent:

```
<$action-setfield $field="myfield" $value="abc 123"/>
```

```
<$action-listops $field="myfield" $filter="abc 123"/>
```

In general, ActionSetFieldWidget is better for setting multiple fields at once and for replacing a field's value. The ActionListopsWidget is better for modifying a field based on the field's existing value and for using a [[Filter Expression]] to derive the value.

! Extended Filter Operators

A number of [[extended filter operators|The Extended Listops Filters]] are necessary for the manipulation of lists. These operators have been designed primarily for use in subfilter expressions whereby the modified current list is returned in place of the current list.

<table>
<<.group-heading "Listops Operators">>
<tr>
<th align="left">Operator</th>
<th align="left">Purpose</th>
<th></th>
</tr>
<<.operator-rows "[tag[Filter Operators]tag[Listops Operators]tag[Order Operators]!tag[String Operators]!tag[Tag Operators]!tag[Special Operators]sort[]]">>
</table>

! Examples

In this example we shall populate and then clear a list in an ordinary field (myfield) of this tiddler (the default.)

<$macrocall $name='wikitext-example-without-html'
src="""<$button>
<$action-listops $field="myfield" $subfilter="efg hlm pqr"/>
Populate 'myfield'
</$button>
<$button>
<$action-listops $field="myfield" $subfilter="abc xyz"/>
Append More Items
</$button>
<$button>
<$action-listops $field="myfield" $subfilter="-abc -hlm"/>
Remove Items
</$button>
<$button>
<$action-listops $field="myfield" $filter="[[]]"/>
Clear 'myfield'
</$button>

<$list filter="[list[!!myfield]]">

</$list>"""/>

---
In this example we shall append and remove items from a list in an ordinary field (myfield) of this tiddler (the default) and sort the resultant list. We shall then remove some of the appended items and sort the resulting list in reverse order.

<$macrocall $name='wikitext-example-without-html'
src="""<$button>
<$action-listops $field="myfield" $subfilter="-efg ijk xyz [[this is a title]] +[sort[]]"/>
Mangle List
</$button>
<$button>
<$action-listops $field="myfield" $subfilter="-xyz -[[this is a title]] +[!sort[]]"/>
Unmangle List
</$button>

<$list filter="[list[!!myfield]]">

</$list>"""/>

---
In this example we shall append a few tags to the 'tags' field of this tiddler (the default.) We shall then remove some of the appended tags. 

<$macrocall $name='wikitext-example-without-html'
src="""<$button>
<$action-listops $tags="+[append{Days of the Week!!short}] $:/tag1 $:/tag2 $:/tag3"/>
Populate 'tags'
</$button>
<$button>
<$action-listops $tags="+[!remove:2{!!tags}]"/>
Remove Last Two Tags
</$button>
<$button>
<$action-listops $tags="+[!prefix[$:/]]"/>
Remove System Tags
</$button>
<$button>
<$action-listops $tags="-Mon -Tue"/>
Remove Mon and Tue
</$button>
<$button>
<$action-listops $tags="+[prefix[$:/]] ActionWidgets Widgets"/>
Remove User Tags
</$button>
<$button>
<$action-listops $tags="+[[]] ActionWidgets Widgets"/>
Clear Tags
</$button>

<$list filter="[list[!!tags]]">

</$list>"""/>