Google Charts: passing dates without using Date()?

Question

Summary

I'm trying to make a line graph in Google Charts with dates as the X axis. I have that all sorted but it requires passing dates as Date objects, i.e. new Date(2005, 3, 13). Is there any way I can pass it as a Unix timestamp or perhaps a string instead?

More Details

So I have a bunch of data in PHP that I want to graph. I'm taking the data and arranging it into an array in the format that will produce the correct JSON format when run through json_encode(), per the Google data docs:

$graph_data = array(
    'cols' => array(
        array(
            'id' => 'date',
            'label' => 'Date',
            'type' => 'datetime',
        ),
        array(
            'id' => 'odometer',
            'label' => 'Miles',
            'type' => 'number',
        ),
    ),
    'rows' => array(
        array(
            'c' => array(
                array( 'v' => 1331479502 ),
                array( 'v' => 56872 ),
            ),
        ),
        array(
            'c' => array(
                array( 'v' => 1331375984 ),
                array( 'v' => 55324 ),
            ),
        ),
        array(
            'c' => array(
                array( 'v' => 1328966460 ),
                array( 'v' => 54244 ),
            ),
        ),
    ),
);

{"cols":[{"id":"date","label":"Date","type":"datetime"},{"id":"odometer","label":"Miles","type":"number"}],"rows":[{"c":[{"v":1331479502},{"v":56872}]},{"c":[{"v":1331375984},{"v":55324}]},{"c":[{"v":1328966460},{"v":54244}]}]}

So I have the JSON creation down but the API wants dates passed as a Date object and not a number (or string). It throws an error right now but if I change it from datetime to number, it graphs perfectly so I know my JSON format is correct.

Is there anything I can do to have the API accept Unix timestamps, or perhaps a string of some sort?

As I typed this out, I realized that perhaps I could use some Javascript to walk the JSON object and replace the timestamps with Date objects, but it'd be nice if I didn't have to do any data manipulation via Javascript.

EDIT

I got part of the way there by setting the type to number and passing dates like this:

        array(
            'c' => array(
                array( 'v' => 1331479502, 'f' => 'March 11th, 2012' ),
                array( 'v' => 56872 ),
            ),
        ),

That makes the f value show up in the tooltip (yay!) but the v value is still used for the axis labels. Hmm.

EDIT #2

Looks like there might be some potential in using DataView to transform a number timestamp into a date but I haven't figured it out yet.

Answer 1

I ended up just walking the JSON array and replacing the timestamps with Date objects. It was easier than I expected it to be:

for ( var i = 0; i < json.rows.length; i++ ) { 
    json.rows[i].c[0].v = new Date( json.rows[i].c[0].v * 1000 );
}