The LINQ query below is working fine but I need to tweak it a bit.
I want all the records in the file grouped by recordId (a customer number) and then ordered by, in descending order, the date. I'm getting the grouping and the dates are in descending order. Now, here comes the tweaking.
I want the groups to be sorted, in ascending order, by recordId. Currently, the groups are sorted by the date, or so it seems. I tried adding a .OrderBy after the .GroupBy and couldn't get that to work at all.
Last, I want to .take(x) records where x is dependent on some other factors. Basically, the .take(x) will return the most-recent x records. I tried placing a .take(x) in various places and I wasn't getting the correct results.
var recipients = File.ReadAllLines(path)
.Select (record => record.Split('|'))
.Select (tokens => new
{
FirstName = tokens[2],
LastName = tokens[4],
recordId = tokens[13],
date = Convert.ToDateTime(tokens[17])
}
)
.OrderByDescending (m => m.date)
.GroupBy (m => m.recordId)
.Dump();
Edit #1 -
recordId is not unique. There may / will likely be multiple records with the same recordId. recordId is actually a customer number.
The output will be a resultset with first name, last name, date, and recordId. Depending on several factors, there many be 1 to 5 records returned for each recordId.
Edit #2 -
The .Take(x) is for the recordId. Each recordId may have multiple rows. For now, let's assume I want the most recent date for each recordId. (select top(1) when sorted by date descending)
Edit #3 -
The following query generates the following results. Note each recordId only produces 1 row in the output (this is okay) and it appears it is the most recent date. I haven't thouroughly checked this yet.
Now, how do I sort, in ascending order, by recordId?
var recipients = File.ReadAllLines(path)
.Select (record => record.Split('|'))
.Select (tokens => new
{
FirstName = tokens[2],
LastName = tokens[4],
recordId = Convert.ToInt32(tokens[13]),
date = Convert.ToDateTime(tokens[17])
}
)
.GroupBy (m => m.recordId)
.OrderByDescending (m => m.Max (x => x.date ) )
.Select (m => m.First () )
.Dump();
FirstName LastName recordId date
X X 2531334 3/11/2011 12:00:00 AM
X X 1443809 10/18/2001 12:00:00 AM
X X 2570897 3/10/2011 12:00:00 AM
X X 1960526 3/10/2011 12:00:00 AM
X X 2475293 3/10/2011 12:00:00 AM
X X 2601783 3/10/2011 12:00:00 AM
X X 2581844 3/6/2011 12:00:00 AM
X X 1773430 3/3/2011 12:00:00 AM
X X 1723271 2/4/2003 12:00:00 AM
X X 1341886 2/28/2011 12:00:00 AM
X X 1427818 11/15/1986 12:00:00 AM
You can't that easily order by a field which is not part of the group by fields. You get a list for each group. This means, you get a list of date for each recordId.
You could order by Max(date) or Min(date).
Or you could group by recordId and date, and order by date.
order by most recent date:
.GroupBy (m => m.recordId)
// take the most recent date in the group
.OrderByDescending (m => m.Max(x => x.date))
.SelectMany(x => x.First
The Take part is another question. You could just add Take(x) to the expression, then you get this number of groups.
Edit:
For a kind of select top(1):
.GroupBy (m => m.recordId)
// take the most recent date in the group
.OrderByDescending (m => m.Max(x => x.date))
// take the first of each group, which is the most recent
.Select(x => x.First())
// you got the most recent record of each recordId
// and you can take a certain number of it.
.Take(x);
snipped I had before in my answer, you won't need it according to your question as it is now:
// create a separate group for each unique date and recordId
.GroupBy (m => m.date, m => m.recordId)
.OrderByDescending (m => m.Key)
This seems very similar to your other question - Reading a delimted file using LINQ
I don't believe you want to use Group here at all - I believe instead that you want to use OrderBy and ThenBy - something like:
var recipients = File.ReadAllLines(path)
.Select (record => record.Split('|'))
.Select (tokens => new
{
FirstName = tokens[2],
LastName = tokens[4],
recordId = tokens[13],
date = Convert.ToDateTime(tokens[17])
}
)
.OrderBy (m => m.recordId)
.ThenByDescending (m => m.date)
.Dump();
For a simple Take... you can just add this .Take(N) just before the Dump()
However, I'm not sure this is what you are looking for? Can you clarify your question?
just add
.OrderBy( g=> g.Key);
after your grouping. This will order your groupings by RecordId ascending.
Last, I want to .take(x) records where
x is dependent on some other factors.
Basically, the .take(x) will return
the most-recent x records.
If you mean by "the most recent" by date, why would you want to group by RecordId in the first place - just order by date descending:
..
.OrderByDescending (m => m.date)
.Take(x)
.Dump();
If you just want to get the top x records in the order established by the grouping though you could do the following:
...
.GroupBy (m => m.recordId)
.SelectMany(s => s)
.Take(x)
.Dump();
If you want something like the first 3 for each group, then I think you need to use a nested query like:
var recipients = File.ReadAllLines(path)
.Select(record => record.Split('|'))
.Select(tokens => new
{
FirstName = tokens[2],
LastName = tokens[4],
RecordId = tokens[13],
Date = Convert.ToDateTime(tokens[17])
}
)
.GroupBy(m => m.RecordId)
.Select(grouped => new
{
Id = grouped.Key,
First3 = grouped.OrderByDescending(x => x.Date).Take(3)
}
.Dump();
and if you want this flattened into a record list then you can use SelectMany:
var recipients = var recipients = File.ReadAllLines(path)
.Select(record => record.Split('|'))
.Select(tokens => new
{
FirstName = tokens[2],
LastName = tokens[4],
RecordId = tokens[13],
Date = Convert.ToDateTime(tokens[17])
}
)
.GroupBy(m => m.RecordId)
.Select(grouped => grouped.OrderByDescending(x => x.Date).Take(3))
.SelectMany(item => item)
.Dump();
Related
I have a DataTable (dtResult) with 4 fields, id, store, sku and qty. Unfortunately there are a lot of duplicates in the DataTable that I want to remove (qtys are diff, but other fields are the same).
I want to sort the DataTable by id asc, store asc, sku asc, and group by id, store and sku so I would have a list of unique records.
IDEALLY I would like to overwrite the existing DataTable with the results of the query, and qty can just be 0 for everything. I have the sort, and currently I'm putting it into a new DataTable:
var dtUniqueResults = dtResult.AsEnumerable()
.OrderBy(r => r.Field<string>("id"))
.ThenBy(r => r.Field<string>("store"))
.ThenBy(r => r.Field<string>("sku"))
.CopyToDataTable();
I don't understand how to group with LINQ. I think I need to add something like this, but it's not working.
var dtUniqueResults = dtResult.AsEnumerable()
.GroupBy(n => n.Field<string>("id"),
n => n.Field<string>("store"),
n => n.Field<string>("sku")
)
.OrderBy(r => r.Field<string>("id"))
.ThenBy(r => r.Field<string>("store"))
.ThenBy(r => r.Field<string>("sku"))
.CopyToDataTable();
I've read a lot of posts, and I see several ways of doing it. However it seems the two that are suggested the most are these, but they seem so different it just confuses me more.
GroupBy( x => new { x.Column1, x.Column2 })
AND
GroupBy(x=> new { x.Column1, x.Column2 }, (key, group) => new
{
Key1 = key.Column1,
Key2 = key.Column2,
Result = group.ToList()
});
If you need to filter out duplicates, try the following query:
var dtUniqueResults = dtResult.AsEnumerable()
.GroupBy(n => new
{
Id = n.Field<string>("id"),
Store = n.Field<string>("store"),
Sku = n.Field<string>("sku")
}
)
.SelectMany(g => g.Take(1)) // get from group only one record
.CopyToDataTable();
I have a list where I'm applying the following condition with linQ:
I want to select all items where Name contains a certain string.
var nameFilter = result
.Where(e => e.Name.Contains(requestedValue))
.ToList();
At the end, sometimes it happens that I am having a list with repeated names:
For example:
requestedValue = 'form';
I end up with:
Name Price
transformer 100
transformer 20
formation 340
former 201
I got transformer twice. In that case, I want to only leave transformer with the least price : 20
How could I do this with linQ without looping?
You can take advantage of GroupBy method
var nameFilter = result.Where(e => e.Name.Contains(requestedValue))
.GroupBy(k=>k.Name, g=>g.Price, (k,g)=>new Model {Name = k, Price = g.Min()})
.ToList();
where new Model should be changed to your class name.
If you have more properties to return probably it will be more convenient to do
var nameFilter = result.Where(e => e.Name.Contains(requestedValue))
.GroupBy(k => k.Name, g => g, (k, g) =>
{
var minPrice = g.Min(x => x.Price);
return g.First(x => x.Price == minPrice);
}).ToList();
Finding minPrice and finding the item with minPrice can be done is a single for loop or, for example, by using following discussion here
I am trying to group a list and using ToDictionary to achieve this which works:
var levels = ids.GroupBy(f => f.Id).
ToDictionary(g => g.Key, g => g.First().Name);
The problem is: in the string "Name" the last char is a number i.e. 2 or 5 or 7 etc.
I do NOT want to select the first but I want to select "Name" with the MAX number. How can i achieve this. example of Name can be: "abd-hbb-les3" , "abd-hbb-les1" , "abd-hbb-les6"
You could do this in the following way:
var levels = ids.GroupBy(f => f.Id).ToDictionary(g => g.Key,
g => g.First( x=> x.Name.Last() == g.Max( y=> y.Name.Last())).Name);
assuming that it's really about the last letter so it's not possible to have a two (or more) digits at the end e.g.:
abd-hbb-les16 //will not work with the above code
For every group simply select the name with the maximum last character of the string. Like this:
var levels = ids.
GroupBy(f => f.Id).
ToDictionary(
g => g.Key,
g => g.First(i => i.Name.Last() == g.Max(j => j.Name.Last())).Name);
How would I write a LINQ query to do the following?
I have a database table with a schema like this:
ID - Int
Time - DateTime
RecordType - Int
Msg - String
I want to get the newest (using 'Time' field) record for each 'RecordType'
Another restriction is that I'm only interested in certain RecordTypes - those contained in an int array.
The result of the query would be one record per RecordType - the newest record for this type.
var results = source.GroupBy(x => x.RecordType)
.Where(g => myRecordTypes.Contains(g.Key))
.Select(g => g.OrderByDescending(x => x.Time).First())
.ToList();
myRecordTypes is int[] with a set of RecordTypes you'd like to get as a result.
result will be List<Record> with one item per RecordType.
You can change to it to be e.g. Dictionary<int, Recort> by RecordType:
var results = source.GroupBy(x => x.RecordType)
.Where(g => myRecordTypes.Contains(g.Key))
.Select(g => new { g.Key, item = g.OrderByDescending(x => x.Time).First() })
.ToDictionary(x => x.Key, x => x.item);
Group them by record types, filter out the ones you want, and then select out the first of the items in that group ordered by time.
int[] recordTypes = GetRecordTypes();
var query = context.Table.GroupBy(item => item.RecordType)
.Where(group => recordTypes.Contains(group.Key))
.Select(group => group.OrderBy(item => item.Time).FirstOrDefault());
Code :
news = (from New myNew in new News()
select myNew).Distinct().ToList();
but this Distinct is for "object" with same values. I need, into my list, a myNew for each month. (so one for january, one for februaru, and so on). Than, news will get 12 record.
Is it possible a sort of Distinct(myNew.Month)?
You could group by month and take the first or last or whatever(you haven't told us):
var news = News()
.GroupBy(n => n.Month)
.Select(grp => grp.Last());
Edit: From the comment on Habib's answer i see that you want 12 months even if there are no news. Then you need to do a "Linq Outer-Join":
var monthlyNews = from m in Enumerable.Range(1, 12) // left outer join every month
join n in News() on m equals n.Month into m_n
from n in m_n.DefaultIfEmpty()
group n by m into MonthGroups
select new {
Month = MonthGroups.Key,
LastNews = MonthGroups.Last()
};
foreach (var m in monthlyNews)
{
int month = m.Month;
var lastNewsInMonth = m.LastNews;
if (lastNewsInMonth != null) ; // do something...
}
Edit: Since you have problems to implement the query in your code, you don't need to select the anonymous type which contains also the month. You can also select only the news itself:
var monthlyNews = from m in Enumerable.Range(1, 12) // every motnh
join n in news on m equals n.Month into m_n
from n in m_n.DefaultIfEmpty()
group n by m into MonthGroups
select MonthGroups.Last();
Note that you now get 12 news but some of them might be null when there are no news in that month.
Solution 1. Get MoreLinq (also available as NuGet package and use
News().DistinctBy(n => n.Property)
Solution 2. Implement an IEqualityComparer and use this Distinct() overload.
var result = News()
.GroupBy(p => p.Month)
.Select(g => g.First())
.ToList();
Short hand solution
var vNews = News()
.GroupBy(p => p.Month, (key, p) => p.FirstOrDefault())
.ToList();
var vNews = News()
.GroupBy(p => p.Month)
.Select(g => g.First())
.ToList();