issue_comments: 1247058071

This data as json

html_url issue_url id node_id user created_at updated_at author_association body reactions performed_via_github_app issue
https://github.com/pydata/xarray/issues/7031#issuecomment-1247058071 https://api.github.com/repos/pydata/xarray/issues/7031 1247058071 IC_kwDOAMm_X85KVJiX 35968931 2022-09-14T17:02:46Z 2022-09-14T17:02:46Z MEMBER

That's very helpful, and should definitely go in the docs somewhere!

On Wed, 14 Sep 2022, 11:31 Benoit Bovy, @.***> wrote:

My understanding from reading the docs was that every Dataset.meth calls the corresponding Index.meth.

Yes that's indeed what I've written in #6975 https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_pydata_xarray_pull_6975&d=DwMCaQ&c=009klHSCxuh5AI1vNQzSO0KGjl4nbi2Q0M1QLJX9BeE&r=qdISi9HqjazmE0DcySuXts3OlnplnLfKjH4hpzAV0xo&m=p6AEVnna74Yl7ERqNIUh2N0qdwITIr0EYT0apJ7Hbgk0KdQNUOudgu8tMxoLiNLW&s=aId1i1PHZl_Co87NrwWTHiu6metAHOBNNVBaBQt1LAo&e= and I realize now that this is confusing, especially for isel.

So Dataset.sel calls Index.sel, but can also sometimes call Dataset.isel. But Dataset.isel does not call Index.isel, nor Index.sel.

So we can describe the implementation of Dataset.sel() has a two-step procedure:

1.

remap the input dictionary {coord_name: label_values} to a dictionary {dimension_name: int_positions}. - This is done via calls to Index.sel() for each unique index found in Dataset.xindexes 2.

pass the the dictionary {dimension_name: int_positions} to Dataset.isel(). - Dataset.isel() will itself call Variable.isel() for each variable in Dataset.variables and Index.isel() for each unique index in Dataset.xindexes

This omits a few implementation details (special cases for multi-index), but that's basically how it works.

I think it would help if such "how label-based selection works in Xarray" section was added in the "Xarray internals" documentation, along with other "how it works" section for, e.g., alignment.

— Reply to this email directly, view it on GitHub https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_pydata_xarray_issues_7031-23issuecomment-2D1246944137&d=DwMCaQ&c=009klHSCxuh5AI1vNQzSO0KGjl4nbi2Q0M1QLJX9BeE&r=qdISi9HqjazmE0DcySuXts3OlnplnLfKjH4hpzAV0xo&m=p6AEVnna74Yl7ERqNIUh2N0qdwITIr0EYT0apJ7Hbgk0KdQNUOudgu8tMxoLiNLW&s=Ks6PoxVcaVr7k89uOVteNHQ4LJ6gUn1ONjAA_UVC3PU&e=, or unsubscribe https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_notifications_unsubscribe-2Dauth_AISNPIYBB6EDBNOL3ORUFKLV6HVT3ANCNFSM6AAAAAAQL2WYZI&d=DwMCaQ&c=009klHSCxuh5AI1vNQzSO0KGjl4nbi2Q0M1QLJX9BeE&r=qdISi9HqjazmE0DcySuXts3OlnplnLfKjH4hpzAV0xo&m=p6AEVnna74Yl7ERqNIUh2N0qdwITIr0EYT0apJ7Hbgk0KdQNUOudgu8tMxoLiNLW&s=ojUYzNS_we7kqIG-mT0SDi_iY4nS4fri483cGbjgHwk&e= . You are receiving this because you were mentioned.Message ID: @.***> 

{
    "total_count": 0,
    "+1": 0,
    "-1": 0,
    "laugh": 0,
    "hooray": 0,
    "confused": 0,
    "heart": 0,
    "rocket": 0,
    "eyes": 0
}
   1372035441