Conditional Group and Select in LINQ with type conversion

Conditional Group and Select in LINQ with type conversion

I know there is a bunch of questions out there already on this but I still
cannot get it to work due to the type conversion (I think).
I have a list of custom class and I normally group this either by months
(mt) or by quarters (qr) depending on user choice. This works fine.
However, now I have the request to allow grouping by say Q413 and the rest
of 2013 in months. Mt and Qr are strings. Quartpos is a double and equals
4 if only Q4 is in quarters and rest in months.
Here is what I have:
List<MyClass> results = classlist
.GroupBy(a => new {
a.rg,
a.tar,
a.mt = ((double.Parse(a.qr) < quartpos) ? a.mt : 0),
a.qr })
.Select(g => new MyClass {
RG = g.Select(a => a.rg).First(),
tar = g.Select(a => a.tar).First(),
yr = g.Select(a => a.yr).First(),
qr = g.Select(a => a.qr).First(),
mt = g.Select(a => a.mt).First(),
pp = g.Average(a => double.Parse(a.pp)),
pi = g.Sum(a => double.Parse(a.pi)),
cp = g.Average(a => double.Parse(a.cp)),
ci = g.Sum(a => double.Parse(a.ci)),
it = g.Sum(a => double.Parse(a.it)),
to = g.Sum(a => double.Parse(a.to)),
cnt = g.Select(a => a.dt).Distinct().Count(),
pdvol = g.Sum(a => (double.Parse(a.pp) <= 1)
? 0
: (double.Parse(a.pi) /
double.Parse(a.pp))) })
.ToList();
This throws two errors:
String Int type conversion - since mt is string but : 0 is int
Invalid anonymous type member declaration.
I m fully aware that I would have to use the same syntax in the select to
make sure that quarters are selected if grouped by quarters and months if
grouped by mounths also.
Thanks.