states = Table[Subscript[state, i] , {i, 1, 50}];
dat = RandomReal[{1, 5}, {50, 3}];
mergeddat = Transpose[Prepend[Transpose[dat], states]];
key = Table[Subscript[state, i] , {i, 1, 50, 10}];
mydata =
 Flatten[Table[
    Select[mergeddat, #[[1]] == key[[i]] &], {i, 1, Length[key]}],
   1] // MatrixForm

mydata= Select[mergeddat, MemberQ[key, #[[1]]] &] // MatrixForm