Data for users who have signed up on a particular date

Hi team,

I want to group by signupdate in properties. But the date-data is being recorded as time-stamp eg : 2018-07-15T21:09:23.000Z
Help me extract date out time-stamp.

Here is the query I have written

function main()
{
return Events({from_date:'2018-07-07',to_date: '2018-07-16'})
.filter(function(event) { return event.name == "abc"})

.groupBy(
["name","properties.signupDate"],
mixpanel.reducer.count()
);
}

I would want to get data for the time range 7 July 2018 to 16 July 2018

Thanks