[Feature request] Overlap between collections in my library

I would like to display all the collections which have at least one item in common with the collection currently selected (e.g. "Project 1"). This could be displayed in the right-side pane of the collection (obtained by space bar to deselect any item), currently showing the total number of items in the collection. It could sort the overlapping collections by decreasing number of overlapping items, and also show the total number of items in that collection (something like "Project 2 (6/35)"). Selecting one of the overlapping collections (e.g. "Project 2") could put a different colour background to the overlapping items, to identify the nature of the overlap. Double clicking on one collection could go to that collection, with the original collection selected in the right-side pane, to identify also the items that are in "Project 2" but not in "Project 1". With eventually more tools to compare more than 2 overlapping collections at once, by selecting multiple collections in the library pane or in the right-side pane.
The feature could be automatically displayed, or triggered by pressing and holding Ctrl, in a similar way as from an item, if it uses too much computer resources: https://www.zotero.org/support/collections_and_tags#identifying_collections_an_item_is_in

I am building a bibliography for a project. As I progress, I add the key articles that I can remember for the topics I want to mention in the literature review. For some of these topics, I may have already done the literature review in a previous project. With this feature, as soon as I add the key articles, I would automatically be suggested other collections where I have worked on a similar topic, and may import some additional references from these older projects. Towards the end of the literature review, with the collection growing, I would have a fine overview of the connections with previous projects, showing me very quickly the most related collections I have in my library.

At the moment, I could first search overlapping collections item by item by pressing and holding Ctrl. From there, I could compare selected collections with an advanced search. But this item by item and collection by collection search would require a lot of efforts and time, especially if repeated several times during the literature review.
I feel that having this tool showing the overlapping collections would significantly enhance the literature review process, building on the work that was already accumulated in Zotero from previous projects.
In several cases, I have missed important citations because I could not remember where I had worked on them before. I know that some important references are talking about this topic, and I remember that I have put them in a folder when I was working on a previous project. But I cannot find it, because I don't remember which project it was. This tool will most likely help me avoid this kind of problem. I should be able to recover relevant references, as long as I had stored them in the project collection when I was working on it. The relevant references may be difficult to find from a single item, but would likely emerge from this tool showing an overview of the interconnections between my collections.
  • Tags would do this by default: If you filter by Tag A, the tag selector shows only those tags that co-occur with it (except for colored tags, which I think are always displayed).
  • edited August 22, 2022
    Thank you for your reply.
    As I understand your suggestion, it would mean duplicating the whole folders structure into tags? Or using tags instead of folders to identify separate projects in the first place?

    Even if I use tags, I think it would not show the number of overlapping items? It would also not order them with these numbers?
    The tag selector allows you to quickly show the overlap. But the main purpose here is to show the non-overlapping items in overlapping collections. Could this be done with the tag selector? You could do the "is" and "is not" in an advanced search, but then you can do it on folders as well.

    A functionality similar to the tag selector could be implemented directly for the folders in the left-side pane, by pressing and holding Ctrl to identify the overlapping collections, and showing the overlapping items when selecting multiple collections. But you would still miss the other features mentioned above.
  • As I understand your suggestion, it would mean duplicating the whole folders structure into tags? Or using tags instead of folders to identify separate projects in the first place?
    Yes, exactly.
    The tag selector allows you to quickly show the overlap. But the main purpose here is to show the non-overlapping items in overlapping collections. Could this be done with the tag selector? You could do the "is" and "is not" in an advanced search, but then you can do it on folders as well?
    Right, currently there's no "is not" option in the tag selector. Zotero has talked about and updated tag manager as a near-ish term feature enhancement, but no idea if that'd be included (it has been requested a couple of times before, but it's not exactly a frequent user request)
  • I still feel more comfortable using collections for projects at the moment. And duplicating collections into tags (and keeping them updated) will probably be wasting a lot of time for only partially achieving what I would like to do.

    Maybe the development of an updated tag manager could also add the option to manipulate folders in the same way as tags, to avoid the duplicated information.

    But even with tag functionalities, you would still need to explore all combinations of collections, without any clue of the degree of overlap beforehand. With a large number of collections, this is probably not practical.

    Currently the tag selector would increase the speed to find the overlapping items, but would sacrifice the "is not". So with the current features, the advanced search on collections would still be the easiest solution.

    There is probably a better way to implement the functionalities I have described, to integrate better with tags. But I think that getting faster access to the interconnections between collections could be beneficial.
  • I don't see us doing this, but someone could write a script/plugin for it.
    Zotero has talked about and updated tag manager as a near-ish term feature enhancement, but no idea if that'd be included
    (Tag manager will be something different from the tag selector — a separate window for batch operations, etc.)
  • Thank you for your reply.
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