Numeric position info in $list widget and other filters (working implementation)

[Evan Balster]

Hello!

There's a feature I've wanted to see in TiddlyWiki for a while:  The ability, when using the $list widget, to create a variable corresponding to the position of the current item in the list.  My interest in this feature is to use it for coordinates when generating SVGs.  I took the initiative of making a crude working implementation.  Modifying the list widget proved a bit intimidating, so I implemented a filter operator instead.

The new operator is attached and can be imported to a wiki.  It is called addposition, and formats each title in the input list into some combination of title, list position, list size and customizable delimiters.  The intended use is to glue positions onto each list item and un-glue them later with string operations.

The filter operand is a format string, where T is replaced by the input title, P by the position and N by the size of the list.  The default format (when calling addposition[], no operand) is "P:T".  Prefix notation makes it easy to use the splitbefore operator.

Example code:

<table>

<tr><th>index</th><th>tiddler</th></tr>

<$list variable="item" filter="[all[shadows]regexp[list]sort[title]addposition[P/N:T]]">

<$set name=pos filter="[<item>splitbefore[:]removesuffix[:]]">

<$set name=tiddler filter="[<item>removeprefix<pos>removeprefix[:]]">

<tr>
  <td>^^#^^<<pos>></td>
  <td><<tiddler>></td>
</tr>

</$set>

</$set>

</$list>

</table>

If this function proves useful to others, it might be worth investigating position and/or size variable options in the $list widget itself, which would be somewhat more convenient to use.

[PMario]

That's an interesting approach.
thx for sharing
-m

[Jed Carty]

The list widget is very important to tiddlywiki so any modifications need to be done very carefully. In the past Tobias tried adding an index variable to the widget but it didn't play well with some other parts so it had to be removed. I think that your workaround may be a good alternative.

For many use cases you can get away with just using the before and after operators which is one reason this hasn't gotten more work.

And since you mentioned svg, I am working on making a plugin for snap.svg, my work is here http://ooktech.com/jed/ExampleWikis/SnapSVG/

[Evan Balster]

Yeah, after reading through the list widget's code -- particularly the refresh routine, whose performance would be negatively impacted -- I had an inkling that it might make more sense to make a new widget (EG. $numbered-list) rather than customize the existing one.  I may investigate that later.

– Evan

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[Mat]

@Evan - did you happen to take this further?

..or anyone else?

It is in deed a desirable feature and would make it possible to use the listwidget a bit like arrays.

<:-)

[Evan Balster]

Hey, Mat —

Yes, I implemented it.  I believe that implementation was lost in a hard drive failure, but it wasn't difficult at all...  So perhaps I'll try implementing it again and post my solution here.

[Mat]

@Evan - yes please! That'd be great!

<:-)

[Jeremy Ruston]

Hi Mat

On 31 Jan 2017, at 10:12, Mat <matia...@gmail.com> wrote:

It is in deed a desirable feature and would make it possible to use the listwidget a bit like arrays.

I think Tobias contributed a patch some years ago that added an “index” variable to the list widget. The problem is that it breaks an important optimisation for the list widget whereby existing DOM nodes are reused when entries are added or removed from a list. As I recall it, we decided finally that it would be better in a separate widget.

Best wishes

Jeremy

[Tobias Beer]

Hi Evan,

A very neat trick indeed and something I've been wanting for a while now.

Just realized my plugins tobibeer/make and tobibeer/split
also allow you to achieve the effect, see:

• Counting List Item Iterations @ tb5 (or in the plugin documentation)

Best wishes,

Tobias.

[Evan Balster]

Oh hey --- there's my own numbered list implementation, which was apparently implemented with a filter trick.  Didn't realize that was its own thread.

https://groups.google.com/forum/#!msg/tiddlywiki/13_TTJqEEiw/tMBRblyiBQAJ

– Evan

On Wed, Feb 1, 2017 at 12:08 PM, Evan Balster <ev...@imitone.com> wrote:

Oh hey --- there's my own numbered list implementation, which was apparently implemented with a filter trick.  Didn't realize that was its own thread.

https://groups.google.com/forum/#!msg/tiddlywiki/13_TTJqEEiw/tMBRblyiBQAJ

– Evan Balster

creator of imitone

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[Evan Balster]

Ah wait, no, that's this thread.  Not my brightest moment.

Jeremy, would it be possible to get an unoptimized version of the list widget as a basis for customization?  As it is, it looks like the optimization adds a lot of code complexity and it's a little hard to know what to strip out without a strong understanding of TW's codebase.

[Jeremy Ruston]

Hi Evan

Jeremy, would it be possible to get an unoptimized version of the list widget as a basis for customization?  As it is, it looks like the optimization adds a lot of code complexity and it's a little hard to know what to strip out without a strong understanding of TW's codebase.

I'll try to do it if I have a chance. To be honest, it may be easier to go the other way: to take a generic widget and gradually add the list functionality in bits and pieces.

Best wishes

Jeremy.

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[Mat]

Jeremy or Evan - any follow up on this?  I keep hitting cases where it would be useful. I believe a solution would also function as a kind of array, which should appeal to coders coming here.

Tobias' workaround IS an optoin but it's a bit contrived to explicitly add and deduct stuff for each item. Just generally, I reason that the items have a natural position in the provided filter output that one probably could take advantage of - alternatively; I assume the list widget runs through that number of iterations so some kind of counter could maybe follow along for each iteration...

<:-)

[Steven Schneider]

I'm interested in this also, just ran into a use case and found this thread. Importing large # of pix from flickr and providing a first-previous-next-last nav bar based on shared tag. $count tells me how many, but there isn't a $which, so we could generate "Tiddler X of Y" (Tiddler $which of $count).

//steve.

[Jed Carty]

You can list 'Tiddler m of n' without anything new, the wizard wizard plugin does it. I just used count widgets. https://ooktech.com/TiddlyWiki/WizardWizard/

[Steven Schneider]

Jed, I had a look at WizardWizard, which is pretty cool, I must say. Thanks for doing that.

And thanks especially for pointing me towards your macro. You inspired me to explore the "allbefore" operator, which allows me to generate a Tiddler X of Y, where Y is the number of tiddlers counted by a filter and X is the nth tiddler in the list.

Here is code, which if placed in tiddlers tagged "HelloThere" in tiddlywiki.com will create the desired output:

Tiddler <$count filter="[tag[HelloThere]allbefore:include<currentTiddler>]"/> of <$count filter="[tag[HelloThere]]"/> tagged with <<tag HelloThere>><br>

Thanks,

//steve.

[Evan Balster]

Quick reminder because I managed to forget about this myself at one point:  I did provide a working (if hacky) solution in the OP.  The addposition operator is a fairly low-impact way to achieve this effect, and it doesn't take O(N^2) time to execute.

To review, a filter step addposition[P/N:T] will turn "MyItem" into "13/26:MyItem" if it is the thirteenth of twenty-six items.

– Evan

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