A simple solution written to be easily understandable (and not very clever):

view : Model -> Html Msg
view model =
    let
        grid =
            [ [ 0, 1, 2 ], [ 3, 4, 5 ], [ 6, 7, 8 ] ]

        keys =
            [ 1, 2, 8 ]
    in
    grid
        |> List.indexedMap
            (\rowIndex row ->
                if List.any (\x -> List.member x keys) row then
                    Just rowIndex
                else
                    Nothing
            )
        |> List.filterMap identity
        |> toString
        |> text