How about
julia> unique(mapreduce(x-> split(x, (';', '|', ' ')), vcat, mystrs))
7-element Array{SubString{String},1}:
"SWT1"
"LPT"
"ABC"
""
"NYP"
"ABCD"
"PT"
If you have a much longer collection, and expect to see a lot of repetition in these substrings, you might choose to go with:
mapreduce(x -> Set(split(x, (';', '|', ' '))), union!, mystrs)
which performs the unique step each time (when it forms the Set) rather than once at the end.