How do I filter by date and count these dates using relational algebra (Reframe)? - pandas

Question

I'm really stuck. I read the Reframe documentation https://reframe.readthedocs.io/en/latest/ that's based on pandas and I tried multiple things on my own but it still doesn't work. So I got a CSV file called weddings that looks like this:
Weddings, Date
Wedding1,20181107
Wedding2,20181107
And many more rows. As you can see, there are duplicates in the date column but this doesn't matter I think. I want to count the amount of weddings filtered by date, for example, the amount of weddings after 5 october 2016 (20161005). So first I tried this:
Weddings = Relation('weddings.csv')
Weddings.sort(['Date']).query('Date > 20161005').project(['Weddings', 'Date'])
This seems logical to me but I get a Keyerror 'Date' and don't know why? So I tried something more simple
Weddings = Relation('weddings.csv')
Weddings.groupby(['Date']).count()
And this doesn't work either, I still get a Keyerror 'Date' and don't know why. Can someone help me?
Track trace
KeyError Traceback (most recent call last)
<ipython-input-44-b358cdf55fdb> in <module>()
1
2 Weddings = Relation('weddings.csv')
----> 3 weddings.sort(['Date']).query('Date > 20161005').project(['Weddings', 'Date'])
4
5
~\Documents\Reframe.py in sort(self, *args,
**kwargs)
110 """
111
--> 112 return Relation(super().sort_values(*args, **kwargs))
113
114 def intersect(self, other):
~\Anaconda3\lib\site-packages\pandas\core\frame.py in sort_values(self, by,
axis, ascending, inplace, kind, na_position)
4416 by = by[0]
4417 k = self._get_label_or_level_values(by, axis=axis,
-> 4418 stacklevel=stacklevel)
4419
4420 if isinstance(ascending, (tuple, list)):
~\Anaconda3\lib\site-packages\pandas\core\generic.py in
_get_label_or_level_values(self, key, axis, stacklevel)
1377 values = self.axes[axis].get_level_values(key)._values
1378 else:
-> 1379 raise KeyError(key)
1380
1381 # Check for duplicates
KeyError: 'Date'