subquery question - Mailing list pgsql-sql

I have a table: (date timestamp, id integer, value integer)

What Iam trying to do is to get a result that looks like this:

basically a need to combine these two queries into one:

SELECT    date_trunc('day',date) AS day,   sum(value) AS sum_odd     FROM xyz WHERE    id % 2 = 1    GROUP BY date_trunc('day',date)

SELECT    date_trunc('day',date) AS day,   sum(value) AS sum_even    FROM xyz WHERE    id % 2 = 0    GROUP BY date_trunc('day',date)

I found various ways to do this via unions or joins, but none of them seem efficient, what is the best way to do that ? 

thank you very much

Sebastian