Feature request: filter a number of occurence on a list

[sn0oz]

Would it be possible to filter a number of occurence on a list to reduce further the data size for APIs which don't support pagination ?

For example this JSON:

{
list: [
    { "number": 0 },
    { "number": 1 },
    { "number": 2 },
    { "number": 3 }
    ]
}

filtered with something like:
filter["list"][2]["number"] = true;

would result in:

{
list: [
    { "number": 0 },
    { "number": 1 }
    ]
}

[bblanchon]

Hi @sn0oz,

This feature was requested several times, but I never implemented it because I could not find a satisfying API.
See this older answer for details.

The API you suggest makes sense, but it's too limited and is inconsistent with the existing filter["list"][0]["number"] = true, which includes all the elements.
Moreover, because ArduinoJson uses a dense array (as opposed to sparsed arrays), if a user sets filter["list"][100]["number"] = true, it allocates an array of 100 elements, which is quite a waste of RAM.

A better solution would be to use a query language as I suggested in #1486 (comment).
I'm not against the idea, but I'm afraid this will be a huge work with very little return, and the executable would inflate significantly.

We could also use a predicate instead of a query or filter.
This could be as powerful as the query language but wouldn't require a new parser and keep the code small.
I had this idea on the back of my head for a long time, but I couldn't figure out an intuitive API.

For your particular issue, I think the "deserialization in chunks" technique provides a better solution.

Best regards,
Benoit

[sn0oz]

Hi Benoit, thanks for the detailed reply.
I understand your points, and will look at the deserialization in chuncks technique.
Thanks again for your great work on this library !