Create Matrix from two tables

I have the following issue: I have 2 sheets A and B, each of which has a table indexed by some variable indexA and indexB.

I want to create a matrix in a third sheet C whose columns are indexed by indexA and whose rows are indexed by indexB, such that, whenever I add an entry in sheet A or B, the row/column is automatically added to C. How can this be done?

Optional but desired: autofilters across both rows and columns.

I tried using arrays, but it’s incredibly slow. I think this is because the arrays iterate over the whole column for some reason, and doesn’t automatically stop at the last cell that has content?

Most likely it is better to do this in Base. Setting up proper relations, relationships and insert/update queries may be a challenge, but in the end data integrity and useability will most likely benefit from the effort.

A pivot table may yield the desired “Sheet C” functionality, including filters. Not sure how you would go about it with data from separate sheets ; please provide some detail of your data structure and what you are really trying to accomplish. Note that updating a pivot is not automatic. It requires a couple of mouse clicks.

Also, the use of pivot tables (and similar functionality) depends on what kind of content the body of the “C” matrix will hold. If that grid takes manual input, not extracts from sheets A and B, I guess the pivot table is not what you are looking for.

@keme I want to create really a small spreadsheet to keep track of published results in machine learning. Sheet A contains a list of papers and their proposed models, together with attributes of those. Sheet B contains a list of datasets with attributes. In sheet C I want to collect which papers published results on which datasets, so this is manual entry. C will contain floats

C will contain floats

Don’t understand. (What "floats? What good for?. OK. May be very specific to the use-case.

Anyway: Can you confirm that you only want the indexing frame for the 2D-matrix (one row, one column, and that the matrix itself will be filled by directly entering content?
In this case an answer wouldn’t need to regard the explanations concerning “proposed models together…” and “…with attributes” at all.
The relevant point would then be to keep the 2D-thing synchronized with the index entries in the other two sheets.
Can you assure that any adding of entries in the 2 primary sheets always is done by appending (never by inserting), and that the entries will never be sorted at a later time?
If so you need to assure in addition limits for the numbers of index entries in the primary sheets.
Based on the mentioned assurances the solution would be very simple, not having them rather complicated and hardly achieved without user code.