あなたが何を求めているのかわかりませんが、これはそれかもしれません:
1> Term = {struct,[{<<"1">>,<<"2,3,4">>},{<<"2">>,<<"2,3,4">>}]}.
{struct,[{<<"1">>,<<"2,3,4">>},{<<"2">>,<<"2,3,4">>}]}
2> {struct, PropList} = Term.
{struct,[{<<"1">>,<<"2,3,4">>},{<<"2">>,<<"2,3,4">>}]}
3> Dict = dict:from_list(PropList).
{dict,2,16,16,8,80,48,
{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]},
{{[],[],[],[],[],[],[],[],[],[],[],
[[<<"2">>|<<"2,3,4">>]],
[],[],
[[<<"1">>|<<"2,3,"...>>]],
[]}}}
4> dict:fetch_keys(Dict).
[<<"2">>,<<"1">>]
5> dict:fetch(<<"1">>, Dict).
<<"2,3,4">>