Put an array on the same id

Put the arrays under the same id into an array, which has the following arrays: & nbsp; data [1] 20 & nbsp; data [2] 30 & nbsp; data [1] 40 & nbsp; data [1] 50 & nbsp; data [2] 60 & nbsp; data [3] 70 is divided into the following groups & nbsp; data [1] array (20, 40, put the array under the same id in an array
Ladies and gentlemen,

There are the following arrays:
Data [1] = 20
Data [2] = 30
Data [1] = 40
Data [1] = 50
Data [2] = 60
Data [3] = 70

Divided into the following groups
Data [1] = array (20, 40, 50)
Data [2] = array (30, 60)
Data [3] = array (70)

Ask for algorithms to be highly efficient


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Discussion

It is queried from the database, but cannot be grouped. The efficiency is too low.