Fix invalid data loading code in example

[rinx]

Description:

I fixed the invalid data loading code in example/main.go.
I've already mentioned about it a month ago, but it's not fixed yet.
https://github.com/vdaas/vald/projects/4#card-51586276

HDF5 formatted data of fashion-mnist has its data as float32 values. So it should be loaded as float32.

Related Issue:

nothing

How Has This Been Tested?:

nothing

Environment:

• Go Version: 1.15.7
• Docker Version: 19.03.8
• Kubernetes Version: 1.18.2
• NGT Version: 1.13.1

Types of changes:

• Bug fix [type/bug]
• New feature [type/feature]
• Add tests [type/test]
• Security related changes [type/security]
• Add documents [type/documentation]
• Refactoring [type/refactoring]
• Update dependencies [type/dependency]
• Update benchmarks and performances [type/bench]
• Update CI [type/ci]

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?

Checklist:

• I have read the CONTRIBUTING document.
• I have checked open Pull Requests for the similar feature or fixes?
• I have added tests and benchmarks to cover my changes.
• I have ensured all new and existing tests passed.
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly.

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[kpango]

Does this code depend on the data set?
I remember that it was the SET team that wrote the example, but I think SET was verifying the behavior at the time.
@vankichi can you explain the situation a bit?

[kpango]

On a completely unrelated note, I really like this code in the hdf5 library
https://github.com/gonum/hdf5/blob/master/h5d_dataset.go#L69-L99

[rinx]

Yes it does. For fashion mnist, float32 is correct.

[rinx]

I think SET team didn't check whether the loaded value is correct or not. Maybe they checked just only whether the example code works or not.

[kpango]

hmm, I see but this example code can be overwrite dataset path variable by cli argument so could you please add about comment for the users and also could you please add comment to the docs?

[kevindiu]

BTW how can we verify if the loaded data is correct or not?

[rinx]

Sure. I'll revise it. @kpango

Using HDFView (https://www.hdfgroup.org/downloads/hdfview/), you can see the correct values of the data. @kevindiu

[rinx]

I've added comments about the HDF5 datatype on the examples codes.

Since there's no section about the using dataset in the Getting Started, I didn't edit it.

[kpango]

LGTM