exp show: --json does not respect the --only-changed flag

[mattseddon]

Bug Report

Description

Passing the --only-changed flag to exp show has no effect when provided in conjunction with --json .

Example:

params.yaml:

lr: 0.003
weight_decay: 0
epochs: 15

dvc exp show --only-changed yields (unchanged parameters weight_decay & epochs excluded):

and dvc exp show --only-changed --json (unchanged parameters weight_decay & epochs included for all records):

[{
    "rev": "workspace",
    "name": null,
    "data": {
      "rev": "workspace",
      "timestamp": null,
      "params": {
        "params.yaml": {
          "data": { "lr": 0.003, "weight_decay": 0, "epochs": 15 }
        }
      },
      ....

Reproduce

1. run dvc exp show --only-changed (get expected results)
2. run dvc exp show --only-changed --json (get all unchanged columns)

Expected

Same behaviour with and without the --json flag.

Environment information

Output of dvc doctor:

$ dvc doctor
DVC version: 2.58.1 (pip)
-------------------------
Platform: Python 3.10.6 on macOS-13.3.1-arm64-arm-64bit
Subprojects:
        dvc_data = 0.51.0
        dvc_objects = 0.22.0
        dvc_render = 0.5.0
        dvc_task = 0.2.1
        scmrepo = 1.0.3
Supports:
        http (aiohttp = 3.8.4, aiohttp-retry = 2.8.3),
        https (aiohttp = 3.8.4, aiohttp-retry = 2.8.3),
        s3 (s3fs = 2023.5.0, boto3 = 1.26.76)
Config:
        Global: /Users/mattseddon/Library/Application Support/dvc
        System: /Library/Application Support/dvc
Cache types: reflink, hardlink, symlink
Cache directory: apfs on /dev/disk3s1s1
Caches: local
Remotes: s3
Workspace directory: apfs on /dev/disk3s1s1
Repo: dvc, git
Repo.site_cache_dir: /Library/Caches/dvc/repo/9b2d1355ef26cb2a38a704c54d1f3710

Additional Information (if any):

This is relevant for iterative/vscode-dvc#1994 which should be straightforward to implement (in time for 3.0) if this bug gets fixed.

[mattseddon]

Might not be a priority but thought that I would raise it in case we wanted a version of iterative/vscode-dvc#1994 implemented in time for 3.0.

[daavoo]

This is expected behavior but I guess it was not clear enough.

The logic is applied once the raw results (internal repo.experiments.show()) have been converted to a table, similar to other flags like --drop, --kep, --sort.

[dberenbaum]

Agreed it seems like it would be nice @mattseddon.

For whatever flags we ignore, let's mention that in the --json docs.

[dberenbaum]

@mattseddon Let's discuss next meeting whether we want to prioritize showing only changed columns.

A quick look tells me that it's unfortunately not straightforward to do ☹️

[mattseddon]

Turns out this isn't that difficult to do in the extension (iterative/vscode-dvc#4402).