Block orientation data value missing

To set a block, for example a dropper, with an orientation facing up, down, north, south, east, or west, in 1.12.2 you would do it like this:
/setblock ~ ~ ~ minecraft:dropper 3
in 1.13pre-7, you would do it like this:
/setblock ~ ~-1 ~ minecraft:dropper[facing=south]
but there is no way to set the data value of an existing block to a certain orientation?
I have tried things like /data get block ~ ~ ~ {facing:south} and /data get block ~ ~ ~ [facing=south], and nothings works! By putting the [facing=south] next to the dispenser, it implies that there must be a data value for it, but there is not.