Add Extra User Defined Filter Run to Other Predefined Filter Runs

#1

Assume I have a shadow tiddler where user is not recommended to touch it. For example

<$list filter="[tag[Learning]]">

</$list>

I wish to pass an extra user defined filter (stored in a tiddler or variable) to further process the first filter. The simple solution is to use subfilter, so if the original code is written like below

<$list filter="[tag[Learning]]  :and[subfilter<user-filter>]"  >

</$list>

This works fine, but fails if user-filter is not defined. One work around is to use defualt value like [all[]] but I am looking for better solution.

In summary: how can I add a user defined filter run (may have many step) to a predefined filter?

Note: The above example can be tested on tiddlywiki.ocm

download User-Defined-Filter-Extra-Filter.json (392 Bytes)
and open Test My-Template, try to change the user-filter

#2

An old school solution is to wrap the code inside a macro and pass extra filter like below

\define test-extra-filter(user-filter)
<$list filter="[tag[Learning]] $user-filter$"  >

</$list>
\end

This way, user-filter can be undefined. But I consider this a bad practice.

You can also use below macro which is better than above

\define test-extra-filter(user-filter:"[all[]]")
<$list filter="[tag[Learning]]  :and[subfilter<__user-filter__>]"  >

</$list>
\end

BUT, what we can do without using a macro?

#3

Hi @Mohammad ,

Since we can’t directly provide the else operator with a [subfilter[]] operand, we can reverse the logic thanks to the map:flat operator:

<$let user-filter="[all[]prefix[How]]" default-filter="[all[]]">
<$list filter="[<user-filter>!is[blank]else<default-filter>] 
    :map:flat[all[tiddlers+shadows]tag[Learning]subfilter<currentTiddler>]"  >

</$list>
</$let>

First we decide which filter will be used, then we map all the input tiddlers on the chosen filter.

#4

Or maybe more generic:

<$let user-input=    "[tag[Learning]]" 
      user-filter=   "[all[]prefix[How]]" 
      default-filter="[all[]]">
<$list filter="[<user-filter>!is[blank]else<default-filter>] 
      :map:flat[all[tiddlers+shadows]subfilter<user-input>subfilter<currentTiddler>]" >

</$list>
</$let>
2 Likes
#5

As @xcazin had pointed you would need to wrap your list inside of the declaration of the variable user-filter.

In this cases $set widget is useful. In your example, it would be something like:

<$set name="user-filter" filter="[{filterTiddler}]" value={{filterTiddler}} emptyValue="[]">
<$list filter="[tag[Learning]]  :and[subfilter<user-filter>]"  >

</$list>
</$set>

Where filterTiddler would be the tiddler that stores the filter expression.

2 Likes
#6

Thank you @xcazin. Both works specially for cases I want where a modifier operator is used.

1 Like
#7

Thank you @Alvaro.

I just modified the filter="[{filterTiddler}]" to filter="[subfilter{filterTiddler}]"

Your solution works and it can accept more complex filter runs as it uses a separate run through :and

One cavet is with :and it forces its input as final output! so, if user gonna filter the selection (here [tag[Learning]] he/she should take care to not produce extra titles through filterTiddler.

#8

:thinking: Why? The filter is only for check that the filter outpot isn’t empty. Then the filter expression will be used has paramenter of subfilter operator.

#9

The reason is to have code working when filterTiddler is missing or filterTiddler is empty!

1 Like
#10

I think this also should be emptyValue="[all[]]" to pass the previous result intact when nothing is specified by user!

1 Like
#11

My mistake, I didn’t specificy correctly the doubt. The doubt is around of use of subfilter in filter="[subfilter{filterTiddler}] but now I see it the same that a tricky version of [[filterTiddler]!is[missing]!is[blank]]

1 Like