Bad JSON diff when removing object in array of object

[LouisNoailles]

What is the issue you have?

In this test A simple remove is expected as a diff. But the following exemple is not following the expected behavior: Old JSON:

{
    "a": ["aa", "ab"]
}

New JSON:

{
    "a": ["ab"]
}

The JSON Patch:

[
    {
        "op": "remove",
        "path": "/a/1"
    },
    {
        "op": "replace",
        "path": "/a/0",
        "value": "ab"
    }
]

Please describe the steps to reproduce the issue.

1. Create a JSON array containing multiple objects
2. Remove an object but not the last one

What is the expected behavior?

The patch should be as following:

[
    {
        "op": "remove",
        "path": "/a/0"
    }
]

And what is the actual behavior instead?

The JSON Patch is currently as follow:

[
    {
        "op": "remove",
        "path": "/a/1"
    },
    {
        "op": "replace",
        "path": "/a/0",
        "value": "ab"
    }
]

Which version of the library did you use?

Version: 3.9.1

[nlohmann]

I can confirm that the calculated patch is not the shortest one. However, it is correct, thus I removed the "bug" label. The currently implemented diff algorithm is not optimal. PRs welcome.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[yunxuo]

I have the same trouble. for multi-level json example： They're just in a different order. base json:

{
  "cost":[
    {"count":0,"ccc":16.0},
    {"count":2,"ccc":13.0}
  ]
}

target json:

{
  "cost":[
    {"count":2,"ccc":13.0},
    {"count":0,"ccc":16.0}
  ]
}

patch result:

[
  {
    "op": "replace",
    "path": "/status/cost/0/ccc",
    "value": 16.0
  },
  {
    "op": "replace",
    "path": "/status/cost/0/count",
    "value": 0
  },
  {
    "op": "replace",
    "path": "/status/cost/1/ccc",
    "value": 13.0
  },
  {
    "op": "replace",
    "path": "/status/cost/1/count",
    "value": 2
  }
]

Is it possible to provide a good diff algorithm that considers these two jsons to be the same？ Looking forward to your reply！^_^

[gregmarr]

Those two JSON files are not the same. Order of arrays is preserved in JSON. Order of elements in an object is not.

These two are equivalent:

 {"count":0,"ccc":16.0},

 {"ccc":16.0,"count":0},

These two are not:

[1,2,3,4,5,6,7,8,9,10]

[10,9,8,7,6,5,4,3,2,1]