First, your notation for array is misguided.
notation for arrays is [ ].
If you want only remove, reducing the size of your Data array, try this:
Data = [1.2, 3.4, 6.7];
Cat = [1, 4, 1];
Data(Cat == 1) = [];
Your output will be:
Data =
3.4
Accept the answer if that helps.
Cheers
