就是有三个人:a,b, c. 每个人有两个特征:feature1, feature2
old:
feature a b c
-------------------------------------------
feature1 1 3 5
feature1 2 4 6
new:
feature column1
---------------------------------
feature1 1
feature2 2
feature1 3
feature2 4
feature1 5
feature2 6



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