Counting when row has certain condition

I am trying to make this kind of book
1st sheet has like 50 columns and like 1500 rows.

2nd sheet has summary of individual rows, based on key value, so there is like 100 rows times 50 columns times some amount of areas. That amount of areas depends on 1st sheet's "key"-column.

Every row has some key. This "key"-column is in the 1st sheet in certain column. Now I would like to pick up every single row from 1st sheet to 2nd sheet, so that every row with different key value would be listed separately (like if I would "hide" all but one key-"group" at a time). Then I need to calculate vaste amount of numbers from each key area, but I can do that once I get this "picking" done.

For publishing it is important that I can "pick" one-by-one all key areas and show only those.
I don't know how many different values there are in this key area.

So here is an example
1st sheet:
A B C D E F G H
1 2 3 4 5 6 7 8
1 8 7 6 5 4 3 2
2 8 2 7 3 9 4 7
2 4 7 5 6 1 5 7
3 5 6 4 7 8 5 4
4 8 4 7 5 6 8 4

Now having this A-column as the key column, sheet 2 should look like

Values for 1
B C D E F G H
2 3 4 5 6 7 8
8 7 6 5 4 3 2

Values for 2
B C D E F G H
8 2 7 3 9 4 7
4 7 5 6 1 5 7

Values for 3
B C D E F G H
3 5 6 4 7 8 5 4

Values for 4
B C D E F G H
8 4 7 5 6 8 4

So how do I do formula like "Include whole row if that row's this cell has this value"?

If it is too hard to automatize making that new key-"group", I can do that manually. There will be around 30 different values for the key.