Working with date columns

[peterewills]

FIrst off, thanks for building this - it's making my life a lot easier when I work with data in Observable 😄

I'm having some trouble working with dates. I build a data table via

df = aq.from([
  { date: '2020-01-01 00:00:00.000' },
  { date: '2020-01-02 00:00:00.000' }
])

I then add a custom function to shift the date forward 30 days, using moment:

let shiftDateFunc = d => moment(d).add(30, 'days').format()
aq.addFunction("shiftDate", shiftDateFunc)

However, when I try to do

df.derive({shiftedDate: op.shiftDate('date')})

I get an error:

Expression parse error: Invalid date

Which is surprising, since I can map this function over the objects just fine:

df.objects().map(d => shiftDateFunc(d.date)) // succeeds, returns an array of strings

Why can I map this function over the object arrays successfully, but it fails when I register it via addFunction? In my mental model the success of the former should imply that the latter will also work, but obviously I'm confused about something.

[jheer]

How about this instead? (The op special syntax with string column names is defined only for aggregate and window functions...)

df.derive({shiftedDate: d => op.shiftDate(d.date)})

[peterewills]

That did it! Thanks!