guava - Create Multimap from Map<K,Collection<V>> with key as V[0] and value as K using Java 8 -

i have map<string,list<string>>(say inputmap) , want convert map<string,list<string>> each (k,v) in new map (v.get(0),k) of inputmap.

ex.

x -> b,c,d y -> b,d,e z -> b,g,h p -> a,b,d q -> a,d,f r -> a,c,b 

to

b->x,y,z a->p,q,r 

i thought using like

inputmap.entryset().stream().collect(collectors.tomap(map.entry::getvalue.get(0),map.entry::getkey)); 

and converting map multimap, cannot write map.entry::getvalue.get(0)

it great if create multimap in .collect() itself.

you can collect directly multimap:

multimap<string, string> result = inputmap.entryset().stream()         .collect(                 arraylistmultimap::create,                 (mm,e) -> mm.put(e.getvalue().get(0), e.getkey()),                 multimap::putall         );