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How to concat string in LinQ group

var list = Table
.GroupBy(t => t.GroupId, (key, g) => new {key, g})
.Select(t => new Transaction
{
Date = t.g.First().DateCreate,
Reference = $"{t.g.First().AccounttName} {t.g.Select(z => z.DocumentNo)}",
TotalAmount = t.g.Sum(x => x.y.Amount.Value),
})
When grouping with linQ I know how to get a single value with First(), sum with Sum() but what should I do to concact a string value?
In my example how can I merge all my DocumentNo?

Use string.Join:
Reference = $"{t.g.First().AccounttName} {string.Join(",",t.g.Select(z => z.DocumentNo))}"

Store value in dictionary or retrieve from concatened key

I have a dictionary that aggregates the same items and sum a specific value from:
var test = list.GroupBy(x => new { ID=x.ItemID, Uti=x.UtilityName })
.ToDictionary(x => x.Key,
x => x.Sum(t => Convert.ToDecimal(t.EnergyConsumptionQt)
));
This returns a dictionary with a key value that is a concatenation of string ID and string Uti.
I would like to either:
Create a Dictionary<string, decimal> in which the key is the combination / concatenation ItemID+UtilityName (ID + Uti), or a way to get the values from the test variable above, as the current one I do not know how to specify the value I want from as everything that I try returns: cannot convert 'X' to ''.

Do it this way:
var test = list.GroupBy(x => new { ID=x.ItemID, Uti=x.UtilityName })
.ToDictionary(x => x.Key.ID.ToString()+x.Key.Uti,
x => x.Sum(t => Convert.ToDecimal(t.EnergyConsumptionQt)
));

The problem with your initial approach is that the annonymous type is a reference type so the dictionary uses the reference as a key (rather than the values you want to be combined).
As such if you subsequently try to accesss an element with for example:
var elem = test[new {ID=1, Uti="myUtiName"}]
then you actually create a NEW object which does not exist in test so you would get a KeyNotFoundException thrown.
If you use a value type for your dictionary key instead then the dictionary will behave as you are expecting. Perhaps have a struct - something like this maybe:
struct DictKey
{
public string UtilityName { get; set; }
public int Id { get; set; }
}
then your test variable can be initialised with:
var test = list
.GroupBy(x => new DictKey { Id=x.ItemID, UtilityName=x.UtilityName })
.ToDictionary(x => x.Key,
x => x.Sum(t => Convert.ToDecimal(t.EnergyConsumptionQt)));
and you can access it's elements with something like:
var elem = test[new DictKey{Id=1, UtilityName="myUtiName"}]

How to populate a Class with Dictionary using LINQ

In my project I use an XML to import various instances of a class.
I need to import in a List.
The problem is how to import all "dynamicDrop" in a Dictionary:
XML:
<LootProfile name="volpeNormale">
<dynamicDropNumber>3</dynamicDropNumber>
<dynamicDrop>70</dynamicDrop>
<dynamicDrop>40</dynamicDrop>
<dynamicDrop>10</dynamicDrop>
<dynamicTypeArmor>33</dynamicTypeArmor>
<dynamicTypeWeapon>33</dynamicTypeWeapon>
<dynamicTypeConsumable>34</dynamicTypeConsumable>
<dynamicRarityCommon>70</dynamicRarityCommon>
<dynamicRarityUncommon>20</dynamicRarityUncommon>
<dynamicRarityRare>8</dynamicRarityRare>
<dynamicRarityEpic>2</dynamicRarityEpic>
<staticDropNumber>2</staticDropNumber>
<staticDrop idPattern="100">60</staticDrop>
<staticDrop idPattern="145">100</staticDrop>
<faction>All</faction>
<location>All</location>
</LootProfile>
XMLImporter query:
var query = from item in xml.Root.Elements("LootProfile")
select new LootProfile()
{
name = (string)item.Attribute("name"),
dynamicDropNumber = (int)item.Element("dynamicDropNumber"),
dynamicDrop = (Dictionary<int,string>)item.Element("dynamicDrop) //this one doesnt work!
//other element....
}
return query.ToList<LootProfile>();

Here is how you can do it:
var query = xml.Elements("LootProfile")
.Select(item => new LootProfile()
{
name = (string) item.Attribute("name"),
dynamicDropNumber = (int) item.Element("dynamicDropNumber"),
dynamicDrop =
item.Elements("dynamicDrop")
.Select((Item, Index) => new {Item, Index})
.ToDictionary(x => x.Index, x => float.Parse(x.Item.Value))
//other element....
});
var result = query.ToList();
The trick is to use an overload of Select that gives you two lambda parameters; the item itself, and the index of the item.

GroupBy of Anonymous Object strange result

I am getting an unexpected result from GroupBy in this case, I expect a Dictionary<string,List<object>> from GroupBy. But the browser receives something like: [{playdate, experiencetype...}, { ... }, { }], [{playdate, experiencetype,... }, { } ],...
So there are no Keys even though the objects are grouped into arrays, but I want Keys to be there. I put up a breakpoint and checked packagedAjax, and there seems to be a GroupedEnumerable there containing Lookups. Any thoughts?
var packagedAjax = showtimesByMovieAndLocation
.Select(x =>
new
{
playdate = x.PlayDate,
experiencetype = x.FFCode,
vistasessionid = x.SessionID,
areacode = x.AreaCode
})
.GroupBy(x => x.experiencetype);
return new JsonpResult(packagedAjax, Request.QueryString["callback"]);

GroupBy returns an IGrouping, not a Dictionary. If you want a Dictionary, convert it using .ToDictionary():
var packagedAjax = showtimesByMovieAndLocation
.Select(x =>
new
{
playdate = x.PlayDate,
experiencetype = x.FFCode,
vistasessionid = x.SessionID,
areacode = x.AreaCode
})
.GroupBy(x => x.experiencetype)
.ToDictionary(g => g.Key, g => g.ToList());

Linq two select statements, second one uses first ones result,

This linq query works well.
var qry = context.Boxes
.GroupBy(k=>k.Box_ID)
.Select( group => new {
Box_ID = group.Key,
TotalA = group.Sum(p => p.A),
TotalC = group.Sum(p => p.C)
})
.Select(p => new {
Box_ID = p.Kasa_ID,
TotalA = p.TotalA,
TotalC = p.TotalC,
DiffAC = p.TotalA - p.TotalC
});
But, i saw these type select statements, second one uses first select's anonymous type result, written like this:
var qry = context.Boxes
.GroupBy(k => k.Box_ID)
.Select(group => new
{
Box_ID = group.Key,
TotalA = group.Sum(p => p.A),
TotalC = group.Sum(p => p.C)
})
.Select(p => new
{
Box_ID, //*** compiler error
TotalA, //I'm asking about these 3 lines, is this syntax possible
TotalC, //TotalC = p.TotalC,
DiffAC = p.TotalA - p.TotalC // calculate
});
comments contains details.
When i try to compile second query, compiler gives me the error "The name 'Box_ID' does not exist in the current contex".
In fact there is no doubt with first syntax, but second one is more readable. How can i use second syntax? or in which condititons i can use it.

.Select(p => new
{
p.Box_ID,
p.TotalA,
p.TotalC,
DiffAC = p.TotalA - p.TotalC // calculate
});