Get = fun(K, {P}) -> proplists:get_value(K, P) end

It seems that CouchDB wraps property lists in a tuple to flag them as JSON objects:
{Proplist} = {[{< <"this">>, "prop"}, {< <"list">>, "is a JSON object}]}

So you can use proplists:get_value/2 also deep down in your JSON document.
In my example I use Get to make the code more readable.

fun({Doc}) ->
Get = fun(K, L) -> proplists:get_value(K, L) end,
case Get(< <"type">>, Doc) of
< <"usage">> ->
[Year, Month, Day, Hour, Minute | _] = Get(< <"timestamp">>, Doc),
lists:foreach(
fun({Row}) ->
TrackingID = Get(< <"t">>, Row),
In = Get(< <"i">>, Row),
Out = Get(< <"o">>, Row),
Emit([TrackingID, Year, Month, Day, Hour, Minute],[In, Out])
end,
Get(< <"data">>, Doc));
_ ->
ok
end
end.

If you want to emit JSON objects from an Erlang view just do for example

Emit(< <"Example">>, {[{< <"prop">>, "list example"}]})

Rosswart

Thank you,