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/pull/1517#issuecomment-330023238,https://api.github.com/repos/pydata/xarray/issues/1517,330023238,MDEyOklzc3VlQ29tbWVudDMzMDAyMzIzOA==,1386642,2017-09-17T05:56:12Z,2017-09-17T05:56:12Z,CONTRIBUTOR,"Sure. I'd be happy to make a PR once this gets merged.
On Sat, Sep 16, 2017 at 10:39 PM Stephan Hoyer <notifications@github.com>
wrote:

> Alternatively apply_ufunc could see if the func object has a pre_dask_atop
> method, and apply it if it does.
>
> This seems like a reasonable option to me. Once we get this merged, want
> to make a PR?
>
> @jhamman <https://github.com/jhamman> could you give this a review? I
> have not included extensive documentation yet, but I am also reluctant to
> squeeze that into this PR before we make it public API. (Which I'd like to
> save for another one.)
>
> —
> You are receiving this because you were mentioned.
>
> Reply to this email directly, view it on GitHub
> <https://github.com/pydata/xarray/pull/1517#issuecomment-330022743>, or mute
> the thread
> <https://github.com/notifications/unsubscribe-auth/ABUoksuo9P3AJIzemncQQJZ3D5Ga2Opsks5sjLCdgaJpZM4PAViG>
> .
>
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,252358450
https://github.com/pydata/xarray/pull/1517#issuecomment-328358162,https://api.github.com/repos/pydata/xarray/issues/1517,328358162,MDEyOklzc3VlQ29tbWVudDMyODM1ODE2Mg==,1386642,2017-09-10T17:30:19Z,2017-09-10T17:31:18Z,CONTRIBUTOR,"I guess the key issue here is that some computations (E.g. finite differences) cannot be boiled down to passing one numpy function to `atop`. Instead, these calculations consist of three steps: 1) some dask calls, 2) a call to atop, map_blocks, etc, and 3) some more dask calls. In spencer's example, step 1 would be a the call to `da.ghost.ghost` and step 3 would be the call to `da.ghost.trim_internal`. While many dask functions have analogies in XArray,  there are others that do not, such as `da.ghost.ghost`, so it won't always be possible to support this three step class of calculations by replacing the dask calls before and after atop with xarray calls.

@shoyer Would it unreasonably complicated to add some sort of `pre_dask_atop` and `post_dask_atop` arguments to `apply_ufunc`. Alternatively `apply_ufunc` could see if the `func` object has a `pre_dask_atop` method, and apply it if it does.

","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,252358450
https://github.com/pydata/xarray/pull/1517#issuecomment-328356133,https://api.github.com/repos/pydata/xarray/issues/1517,328356133,MDEyOklzc3VlQ29tbWVudDMyODM1NjEzMw==,1386642,2017-09-10T16:59:46Z,2017-09-10T16:59:46Z,CONTRIBUTOR,"Hey Spencer! Thanks. That makes much more sense. I have written nearly identical code for centered differencing, but did not know about `apply_ufunc`, so I had a couple manual calls to `transpose` and `xr.DataArray`. The thing I was hoping for an official way to pass `centerd_diff_numpy` directly to `apply_ufunc`, which would avoid some of the boiler-plate in your `centered_diff` function, which basically rewrites much of the code in this PRs version `apply_ufunc`.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,252358450
https://github.com/pydata/xarray/pull/1517#issuecomment-328326916,https://api.github.com/repos/pydata/xarray/issues/1517,328326916,MDEyOklzc3VlQ29tbWVudDMyODMyNjkxNg==,1386642,2017-09-10T08:10:32Z,2017-09-10T08:11:19Z,CONTRIBUTOR,"Ok thanks. just so I understand you correctly, are you recommending something like this:
    
    xarr_ghosted  =  apply_ufunc(partial(da.ghost.ghost, ...), xarr, dask='allowed',...)
    fd_ghosted = apply_ufunc(finite_difference_func, xarr_ghosted, dask='parallelized',...)
    fd   = apply_ufunc(partial(da.ghost.trim_internal, ...), fd_ghosted, dask='allowed')

Wouldn't xarray complain because the ghosted axes data would have different size than the corresponding coordinates?","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,252358450
https://github.com/pydata/xarray/pull/1517#issuecomment-328275147,https://api.github.com/repos/pydata/xarray/issues/1517,328275147,MDEyOklzc3VlQ29tbWVudDMyODI3NTE0Nw==,1386642,2017-09-09T12:45:21Z,2017-09-09T12:45:21Z,CONTRIBUTOR,"This looks great!

I am not sure if this is the right place to bring this up, but is there any way to add ghost cell functionality to `apply_ufunc` or perhaps to create an `apply_ufunc_ghosted` function. This would be very handy for performing finite differences and filters. I have successfully used `dask.ghost.map_blocks`as well as  `dask.array.ghost.ghost`+`dask.array.core.atop` for this, so I doubtt this would be too hard. ","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,252358450