iris.load() and iris.load_raw() interact differently with iris.util.equalise_attributes() when merging a CubeList

[kaedonkers]

🐛 Bug Report

When using iris.util.equalise_attributes(cubes) before merging a CubeList, I noticed different behaviour based on whether I used iris.load() or iris.load_raw() to generate the CubeList. load_raw() seems to lead to a successful equalisation of the attributes in the CubeList and a successful merge. load() seems to successfully equalisation of the attributes in the CubeList but the merge results in the same as the input CubeList i.e. no merge, despite the input CubeList containing compatible cubes.

How To Reproduce

Successful merge

cubes = iris.load_raw(fnames)
iris.util.equalise_attributes(cubes)
cubes.merge()

Unsuccessful merge

cubes = iris.load_raw(fnames)
iris.util.equalise_attributes(cubes)
cubes.merge()

Data to recreate this issue can be found at: https://metdatasa.blob.core.windows.net/covid19-response/index.html#metoffice_ukv_daily--rain_mean

Specifically:

• ukv_daily_rain_mean_20210327.nc
• ukv_daily_rain_mean_20210329.nc
• ukv_daily_rain_mean_20210330.nc

Expected behaviour

That both cases of the example code return exactly the same merged CubeList.

Screenshots

Environment

• OS & Version: REHL7.9
• Iris Version: 3.0.1

[pp-mo]

Hi Kevin !

I just responded to this. But, we are all very tight on support time due to NG-VAT work, so I doubt I’ll be working on this myself. In a couple of weeks we should be having a bit of a breather from the NG-VAT project, so there might be a bit of space to push this through then.

Cheers ! Patrick

From: Kevin Donkers @.> Sent: 13 April 2021 21:51 To: SciTools/iris @.> Cc: Subscribed @.***> Subject: [SciTools/iris] iris.load() and iris.load_raw() interact differently with iris.util.equalise_cubes.equalise_attributes() when merging a CubeList (#4097)

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🐛 Bug Report

When using iris.util.equalise_attributes(cubes) before merging a CubeList, I noticed different behaviour based on whether I used iris.load() or iris.load_raw() to generate the CubeList. load_raw() seems to lead to a successful equalisation of the attributes in the CubeList and a successful merge. load() seems to successfully equalisation of the attributes in the CubeList but the merge results in the same as the input CubeList i.e. no merge, despite the input CubeList containing compatible cubes.

How To Reproduce

Successful merge

cubes = iris.load_raw(fnames)

iris.util.equalise_attributes(cubes)

cubes.merge()

Unsuccessful merge

cubes = iris.load_raw(fnames)

iris.util.equalise_attributes(cubes)

cubes.merge()

Data to recreate this issue can be found at: https://metdatasa.blob.core.windows.net/covid19-response/index.html#metoffice_ukv_daily--rain_mean

Specifically:

• ukv_daily_rain_mean_20210327.nc
• ukv_daily_rain_mean_20210329.nc
• ukv_daily_rain_mean_20210330.nc

Expected behaviour

That both cases of the example code return exactly the same merged CubeList.

Screenshots

[image]https://user-images.githubusercontent.com/32906197/114618537-5da9aa00-9ca1-11eb-8ef7-99e0c047fabd.png

Environment

• OS & Version: REHL7.9
• Iris Version: 3.0.1

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[rcomer]

Presumably load_raw is returning 24 2D cubes, and merge then creates the new time dimension. load returns a pre-merged list, so the time dimension already exists, so you need concatenate rather than merge to join the two cubes together.

So this could be another one to add to the list at #3234?

[kaedonkers]

Good idea @rcomer - Done :)

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