How to remove duplicate element in the multidimensional passive?

There is, for example, this array:
$array[$i][0] - date
$array[$i][1] - id

It is necessary to make on the same date there was only one id, without repetition
p.s. time is not necessary to include

How best to pull off such an adventure? There were thoughts with cycles, but I don't know whether this is, suddenly there are some better solutions, thank you in advance (:
July 9th 19 at 13:20

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