Json faceting, aggregate numeric field by day?

[Markus Jelsma]

Hi - if we assume the following simple documents:

<doc>
  <date name="time">2015-01-01T00:00:00Z</date>
  <int name="value">2</int>
</doc>
<doc>
  <date name="time">2015-01-01T00:00:00Z</date>
  <int name="value">4</int>
</doc>
<doc>
  <date name="time">2015-01-02T00:00:00Z</date>
  <int name="value">3</int>
</doc>
<doc>
  <date name="time">2015-01-02T00:00:00Z</date>
  <int name="value">7</int>
</doc>

Can i get a daily average for the field 'value' by day? e.g.

<lst name="value">
  <double name="2015-01-01T00:00:00Z">3.0</double>
  <double name="2015-01-02T00:00:00Z">5.0</double>
</lst>

Reading the documentation, i don't think i can, or i am missing it completely. 
But i just want to be sure.

Many thanks,
Markus