I have a simple list
var list =
AppUtils.db.GetDataTable("dbo.RankSelectChart", view) // stopred procedure and getting datatable
.AsEnumerable()
.Select(i => new
{
Date = i.Field<DateTime>("lastDatetime"),
P1 = i.Field<decimal>("p1"),
P2 = i.Field<decimal>("P2"),
P3..... P(n)
}
)
.ToList()
.OrderBy(x => x.Date);
than i want to get a list of lists or dictionary like List<Dictionary<Datetime, Decimal>> means Dictionary<Date, P1> .... Dictionary<Date, P(n)>
how to write algorithm which is not depend how many P we have
As it stands, you will need to use reflection to access the properties:
var result = new[]{"P1", "P2", "P3", ...}.Select(p => list.ToDictionary(
i => i.Date,
i => i.GetType().GetProperty(p).GetValue(i)));
However, if you could avoid creating your list in the first place and just pull from the data table directly, it may be easier.
var dt = AppUtils.db.GetDataTable("dbo.RankSelectChart", view); // stopred procedure and getting datatable
var pColumns = dt.Columns.Cast<DataColumn>()
.Where(c => c.ColumnName.StartsWith("p"));
var result = pColumns
.Select(p => dt.AsEnumerable().ToDictionary(
i => i.Field<DateTime>("lastDatetime"),
i => i.Field<DateTime>(p.ColumnName)))
.ToList();
If 'Date' is unique for all records in 'list', then you can use reflection to get the P(i) value for a record in list. Like so:
// build sample data
var list = Enumerable.Range(0, 10)
.ToList()
.Select(x => new {
Date = DateTime.Now.AddMinutes(x),
P1 = new Decimal(x),
P2 = new Decimal(x + 1),
P3 = new Decimal(x + 2)
})
.ToList();
// list partionned by date; assumes that Date is unique in list
List<Dictionary<DateTime, Decimal>> partitionedList;
if (list.Count == 0) {
partitionedList = new List<Dictionary<DateTime, Decimal>>();
} else {
var n = 3;
var listElementType = list[0].GetType();
partitionedList = Enumerable.Range(1, n)
.Select(x => {
var prop = listElementType.GetProperty("P" + x);
var pList = list.ToDictionary(
ll => ll.Date,
ll => (Decimal)prop.GetValue(ll));
return pList;
})
.ToList();
}
If 'Date' is not unique, then it cannot be the key to a dictionary and the desired data structure is not achievable.
Related
First of all I am new to Linq.
I have a list of objects named Lba that have different properties to be grouped by. My object properties are :
int aId,
int bId,
int max,
int min,
CustomObject1? Co1,
CustomObject2? Co2,
CustomObject3? Co3
I want to group my objects into a new object LbaGroup that have the following properties
int aId,
int bId,
int max,
int min,
IList<CustomObject1> Co1,
IList<CustomObject2> Co2,
IList<CustomObject3> Co3
I grouped my objects with the following query but it returns a List>
var query = myLbaList
.GroupBy(a => new {a.aId, a.bId, a.max, a.min})
.Select(a => a.ToList())
.ToList();
I am able to build my new objects with 2 foreach loops but I was wondering if there is a direct way to achieve that with Linq.
Thank you.
Edit: My loops look like :
foreach(List<Lba> LbaList in query){
LbaGroup myNewObject = new LbaGroup{
Co1 = new List<CustomObject1>(),
Co2 = new List<CustomObject2>(),
Co3 = new List<CustomObject3>(),
}
foreach(Lba oldObject in LbaList){
myNewObject.aId = oldObject.aId;
myNewObject.bId = oldObject.bId;
myNewObject.max = oldObject.min;
if oldObject.Co1 != null
myNewObject.Co1.Add(oldObject.Co1);
if oldObject.Co2 != null
myNewObject.Co2.Add(oldObject.Co2);
if oldObject.Co3 != null
myNewObject.Co3.Add(oldObject.Co3);
}
}
Something like this:
var result = myLbaList
.GroupBy(
a => new {a.aId, a.bId, a.max, a.min}, // Key
a => new {a.Col1, a.Col2, a.Col3}) // Values
.Select(chunk => new {
// From Key
aId = chunk.Key.aId,
bId = chunk.Key.bId,
max = chunk.Key.max,
min = chunk.Key.min,
// From Values
Col1 = chunk
.Where(item => item.Col1.HasValue) // not null items
.Select(item => item.Col1.Value) // CustomObject1? to CustomObject1
.ToList(),
Col2 = chunk
.Where(item => item.Col2.HasValue)
.Select(item => item.Col2.Value)
.ToList(),
Col3 = chunk
.Where(item => item.Col3.HasValue)
.Select(item => item.Col3.Value)
.ToList(),
})
.ToList();
having some trouble writing the following code to some nicer/less lines :)
any one have the good solution?
//custom implementation for popular filters
var popularFilter = new Dictionary<string, int>();
foreach (var car in allFilteredCars)
{
foreach (var offering in car.Offerings)
{
if (popularFilter.ContainsKey(offering))
popularFilter[offering] = popularFilter[offering] + 1;
else
popularFilter.Add(offering, 1);
}
}
categories.Add(new Category
{
Name = "popular",
Code = "popular",
Values = popularFilter.Select(p => new Value
{
Code = p.Key,
Name = p.Key,
Count = p.Value
}).ToList()
});
If it is possible i want i directly to add it in the categories list.
car.offerings = list<string>
so basicly something like:
Categories.Add(allFilteredCars.SelectMany(
c => c.Offerings.Select(
o => new {
something magical here}
.Select(a =>
new Category{
code.. etc etc..}
));
It looks like you just want to do a SelectMany to get the offerings, then group them and select the Count.
categories.Add(new Category
{
Name = "popular",
Code = "popular",
Values = allFilteredCars.SelectMany(c => c.Offerings)
.GroupBy(o => o)
.Select(grp => new Value
{
Code = grp.Key,
Name = grp.Key,
Count = grp.Count()
}).ToList()
});
Your non linq code already looks quite fine.
You can create your dictionary with linq by using a GroupBy & ToDictionary:
var dictionary = offerings
.GroupBy(x => x)
.ToDictionary(x => x.Key, x => x.Count());
I want to make a ranking from a list and output it on original order.
This is my code so far:
var data = new[] { 7.806468478, 7.806468478, 7.806468478, 7.173501754, 7.173501754, 7.173501754, 3.40877696, 3.40877696, 3.40877696,
4.097010736, 4.097010736, 4.097010736, 4.036494085, 4.036494085, 4.036494085, 38.94333318, 38.94333318, 38.94333318, 14.43588131, 14.43588131, 14.43588131 };
var rankings = data.OrderByDescending(x => x)
.GroupBy(x => x)
.SelectMany((g, i) =>
g.Select(e => new { Col1 = e, Rank = i + 1 }))
.ToList();
However, the result will be order it from descending:
What I want is to display by its original order.
e.g.: Rank = 3, Rank = 3, Rank = 3, Rank = 4, Rank = 4, Rank = 4, etc...
Thank You.
Using what you have, one method would be to keep track of the original order and sort a second time (ugly and potentially slow):
var rankings = data.Select((x, i) => new {Item = x, Index = i})
.OrderByDescending(x => x.Item)
.GroupBy(x => x.Item)
.SelectMany((g, i) =>
g.Select(e => new {
Index = e.Index,
Item = new { Col1 = e.Item, Rank = i + 1 }
}))
.OrderBy(x => x.Index)
.Select(x => x.Item)
.ToList();
I would instead suggest creating a dictionary with your rankings and joining this back with your list:
var rankings = data.Distinct()
.OrderByDescending(x => x)
.Select((g, i) => new { Key = g, Rank = i + 1 })
.ToDictionary(x => x.Key, x => x.Rank);
var output = data.Select(x => new { Col1 = x, Rank = rankings[x] })
.ToList();
As #AntonínLejsek kindly pointed out, replacing the above GroupBy call with Distinct() is the way to go.
Note doubles are not a precise type and thus are really not a good candidate for values in a lookup table, nor would I recommend using GroupBy/Distinct with a floating-point value as a key. Be mindful of your precision and consider using an appropriate string conversion. In light of this, you may want to define an epsilon value and forgo LINQ's GroupBy entirely, opting instead to encapsulate each data point into a (non-anonymous) reference type, then loop through a sorted list and assign ranks. For example (disclaimer: untested):
class DataPoint
{
decimal Value { get; set; }
int Rank { get; set; }
}
var dataPointsPreservingOrder = data.Select(x => new DataPoint {Value = x}).ToList();
var sortedDescending = dataPointsPreservingOrder.OrderByDescending(x => x.Value).ToList();
var epsilon = 1E-15; //use a value that makes sense here
int rank = 0;
double? currentValue = null;
foreach(var x in sortedDescending)
{
if(currentValue == null || Math.Abs(x.Value - currentValue.Value) > epsilon)
{
currentValue = x.Value;
++rank;
}
x.Rank = rank;
}
From review of the data you will need to iterate twice over the result set.
The first iteration will be to capture the rankings as.
var sorted = data
.OrderByDescending(x => x)
.GroupBy(x => x)
.Select((g, i) => new { Col1 = g.First(), Rank = i + 1 })
.ToList();
Now we have a ranking of highest to lowest with the correct rank value. Next we iterate the data again to find where the value exists in the overall ranks as:
var rankings = (from i in data
let rank = sorted.First(x => x.Col1 == i)
select new
{
Col1 = i,
Rank = rank.Rank
}).ToList();
This results in a ranked list in the original order of the data.
A bit shorter:
var L = data.Distinct().ToList(); // because SortedSet<T> doesn't have BinarySearch :[
L.Sort();
var rankings = Array.ConvertAll(data,
x => new { Col1 = x, Rank = L.Count - L.BinarySearch(x) });
Is there a way to preserve the order after this linq expression?
var results =
DateList
.GroupBy(x => x.Date.Subtract(firstDay).Days / 7 + 1)
.SelectMany(gx => gx, (gx, x) => new {Week = gx.Key,DateTime =x,Count = gx.Count(),});
I found this Preserving order with LINQ , but I'm not sure if its the GroupBy or SelectMany casing the issues
Yes, if you first select your DateList and combine it with an index, using an overload of .Select that uses a delegate with a second (int) parameter that is called with the index of the items from the sequence :
DateList
.Select((dateTime, idx) => new {dateTime, idx})
.GroupBy(x => x.dateTime.Date.Subtract(firstDay).Days / 7 + 1)
...and persist the value through the linq chain
.SelectMany(gx => gx, (gx, x) => new {Week = gx.Key,
DateTime = x.dateTime,
Count = gx.Count(),
x.idx})
...then use it to re-order the output
.OrderBy(x => x.idx)
...and strip it from your final selection
.Select(x => new {x.Week, x.DateTime, x.Count});
then you can maintain the same order as the original list.
Solution of #spender is good, but can it be done without OrderBy? It can, because we can use the index for direct indexing into array, but it would not be one linq query:
var resultsTmp =
DateList.Select((d, i) => new { d, i })
.GroupBy(x => x.d.Date.Subtract(firstDay).Days / 7 + 1)
.SelectMany(gx => gx, (gx, x) => new { Week = gx.Key, DateTime = x.d, Count = gx.Count(), x.i })
.ToArray();
var resultsTmp2 = resultsTmp.ToArray();
foreach (var r in resultsTmp) { resultsTmp2[r.i] = r; };
var results = resultsTmp2.Select(r => new { r.Week, r.DateTime, r.Count });
It looks a bit complex. I would probably do something more straightforward like:
var DateList2 = DateList.Select(d => new { DateTime = d, Week = d.Subtract(firstDay).Days / 7 + 1 }).ToArray();
var weeks = DateList2.GroupBy(d => d.Week).ToDictionary(k => k.Key, v => v.Count());
var results = DateList2.Select(d2 => new { d2.Week, d2.DateTime, Count = weeks[d2.Week] });
// To get current user id
var currentUsrId = Convert.ToInt16(Membership.GetUser().ProviderUserKey);
var IDquery = My_usr_contacts_requests.Where(i => i.requests_to_usr_id == currentUsrId)
.Select(i => new { i.from_usr_id })
.ToArray();
var mainquery = My_usr_biographic_details
.Join(
My_usr_profiles_companies, i => i.usr_id, j => j.company_usr_id,
(i, j) => new
{
usr_id = j.company_usr_id,
})
.Where(i =>IDquery.contains(i.usr_id))
.ToArray();
while I am executing I am getting array of values in IDquery, and I want to use these values in the where condition of mainquery as shown above, but when I give like this it showing error at the mainquery where condition. Can you tell me how to use the array of values retrieved from IDquery in mainquery?
You wrote:
var IDquery = dbContext.My_usr_contacts_requests.Where(i =>
i.Usr_contacts_requests_to_usr_id==currentUsrId).Select(i => new {
i.Usr_contacts_requests_from_usr_id }).ToArray();
The last new is unnecessary. It creates an array of arrays. You need to change it to:
var IDquery = dbContext.My_usr_contacts_requests.Where(i =>
i.Usr_contacts_requests_to_usr_id==currentUsrId).Select(i =>
i.Usr_contacts_requests_from_usr_id).ToArray();