Evaluation metric using mini-batch

[shejunda]

Description

Checklist

Please feel free to remove inapplicable items for your PR.

• [ ] The PR title starts with [$CATEGORY] (such as [NN], [Model], [Doc], [Feature]])
• [ ] Changes are complete (i.e. I finished coding on this PR)
• [ ] All changes have test coverage
• [ ] Code is well-documented
• [ ] To the best of my knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change
• [ ] Related issue is referred in this PR
• [ ] If the PR is for a new model/paper, I've updated the example index here.

Changes

[shejunda]

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