each operator: Is this a bug?

[Mohammad]

On https://tiddlywiki.com/#each%20Operator%20(Examples)

Look at the first example

[each[color]]

The output result show

$:/library/sjcl.js

But it has no color field!

--Mohammad

[Mark S.]

I don't think it's a bug per se, but it is unintuitive.

From tiddlywiki.com

As long as the value of the field is unique (i.e. has not been encountered before), the title is appended to the output.

and

If a tiddler does not contain field F, it is treated as if the value of the field were empty.

Now use filter

[all[tiddlers]limit[1]]

You'll see that $:/library/sjcl.js is the first item on the list.

So .... when "each" sees the first item in the list tiddlers, it looks at the field "color" in $:/library/sjcl.js. There is no field "color". So it saves the "" value on it's list of values that it has seen, and appends $:/library/sjcl.js
to the output list.

If you delete $:/library/sjcl.js, you'll see that now "each" returns $:/boot/bootprefix.js, which is the next tiddler at tiddlywiki.com.

In real use, you would usually be using "each" in conjunction with "get" or some other filter, so this would not be a problem.

HTH

[Mohammad]

Hi Mark!

 But this is confusing! Why it return one tiddler if there is nothing to return like

[each[nella]]

There is no tiddler has field nella, still we have one at the output?

--Mohammad

[Mohammad]

In real use, you would usually be using "each" in conjunction with "get" or some other filter, so this would not be a problem.

This seem true!

like

[each[nella]get[nella]]

OR

<$list filter="[has[nella]each[nella]get[title]]">

</$list>

--Mohammad

[Mohammad]

Post edited

[Mark S.]

It's looking for unique values of the field. Apparently, "nothing" is a value. So the first tiddler for which the value is "nothing" gets included.

I did say it was unintuitive ;-)

[Mohammad]

I got what you mean Mark!

 So this way always ONE tiddler which has not such field will be included.

Very confusing!  :-)

--Mohammad

[TonyM]

Mohammad,

I was curious when I saw that myself. However even using something like [!is[system]] generates a new false entry.

This needs a Fix

Tony

[Mohammad]

Agree!

[Jeremy Ruston]

Although the current behaviour is confusing, we can’t change it without breaking backwards compatibility. I’ve updated the docs to include a note pointing out a workaround:

Note that if a tiddler does not contain field <<.place F>>, it is treated as if the value of the field were empty. Thus, a filter expression such as `[each[color]]` will return one tiddler that doesn't have a `color` field. To obtain just the tiddlers that have a non-blank value for the `color` field one can use `[each[color]has[color]]`.

https://github.com/Jermolene/TiddlyWiki5/commit/e33d519ce0d78974d7cef80521abe63c131927cc

Best wishes

Jeremy

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[Mohammad]

Hi Jeremy,

 Just for clarification

1. does it has a performance impact if we use [has[color]each[color]] instead of [each[color]has[color]]? which is recommended?
2. How we can separate tiddlers with no field from tiddlers have field but empty?

--Mohammad

On Monday, December 9, 2019 at 12:37:17 PM UTC+3:30, Jeremy Ruston wrote:

Although the current behaviour is confusing, we can’t change it without breaking backwards compatibility. I’ve updated the docs to include a note pointing out a workaround:

Note that if a tiddler does not contain field <<.place F>>, it is treated as if the value of the field were empty. Thus, a filter expression such as `[each[color]]` will return one tiddler that doesn't have a `color` field. To obtain just the tiddlers that have a non-blank value for the `color` field one can use `[each[color]has[color]]`.

https://github.com/Jermolene/TiddlyWiki5/commit/e33d519ce0d78974d7cef80521abe63c131927cc

Best wishes

Jeremy

On 9 Dec 2019, at 06:47, Mohammad <mohamma...@gmail.com> wrote:

Agree!

On Monday, December 9, 2019 at 2:21:36 AM UTC+3:30, TonyM wrote:

Mohammad,

I was curious when I saw that myself. However even using something like [!is[system]] generates a new false entry.

This needs a Fix

Tony

On Monday, December 9, 2019 at 8:07:07 AM UTC+11, Mohammad wrote:

I got what you mean Mark!

 So this way always ONE tiddler which has not such field will be included. 

Very confusing!  :-)

--Mohammad

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[Mohammad]

post edited!

Hi jeremy,

[Jeremy Ruston]

Hi Mohammad

On 9 Dec 2019, at 09:15, Mohammad <mohammad...@gmail.com> wrote:

1. does has a performance impact if we use [has[color]each[color]] instead of [each[color]has[color]]? which is recommended?

I haven’t timed it, but would expect `[each[color]has[color]]` to be quicker under most situations.

2. How we can separate tiddlers with no field from tiddler have field but empty?

I think that may not be currently possible.

Best wishes

Jeremy

[Mohammad]

Thanks Jeremy!