I know this as asked many times but cannot see something that works.
I am reading a csv file and then I have to remove duplicate lines based on one of the columns "CustomerID".
Basically the CSV file can have multiple lines with the same customerID.
I need to remove the duplicates.
//DOES NOT WORK
var finalCustomerList = csvCustomerList.Distinct().ToList();
I have also tried this extension method //DOES NOT WORK
public static IEnumerable<t> RemoveDuplicates<t>(this IEnumerable<t> items)
{
return new HashSet<t>(items);
}
What works for me is
I Read the CSV file into a csvCustomerList
Loop through csvCustomerList and check if a
customerExists If it doesnt I add
it.
foreach (var csvCustomer in csvCustomerList)
{
var Customer = new customer();
customer.CustomerID = csvCustomer.CustomerID;
customer.Name = csvCustomer.Name;
//etc.....
var exists = finalCustomerList.Exists(x => x.CustomerID == csvCustomer.CustomerID);
if (!exists)
{
finalCustomerList.Add(customer);
}
}
Is there a better way of doing this?
For Distinct to work with non standard equality checks, you need to make your class customer implement IEquatable<T>. In the Equals method, simply compare the customer ids and nothing else.
As an alternative, you can use the overload of Distinct that requires an IEqualityComparer<T> and create a class that implements that interface for customer. Like that, you don't need to change the customer class.
Or you can use Morelinq as suggested by another answer.
For a simple solution, check out Morelinq by Jon Skeet and others.
It has a DistinctBy operator where you can perform a distinct operation by any field. So you could do something like:
var finalCustomerList = csvCustomerList.DistinctBy(c => c.customerID).ToList();
Related
I have a List of a Simple Struct that contains int's and strings.
Struct:
public struct ErrorType
{
public int RowNumber;
public int ColumnNumber;
public string ErrorMessage;
}
On of My methods return A list of these structs.
I want to convert each member in the list to its string form and separate it by a comma so that List is now an Array of strings. I could write a function to do this manually but I'd perfer to use linq to have a cleaner solution.
Having the array of strings I'll write it to a file using
string path = #"c:\temp\MyTest.txt";
// This text is added only once to the file.
if (!File.Exists(path))
{
// Create a file to write to.
List<ErrorType> ErrorTypesList = GetErrors();
//do some work to iterate over the members and do a string.join after
string[] ErrorListArray = ErrorTypesList.foreach( e => { });
File.WriteAllLines(path, createText);
}
does anyone have suggestions on how to fill in the foreach so that it returns each members in its ToString form followed by a comma?
The only way you'd be able to use LINQ for property iteration is if you're using reflection, and you shouldn't do that unless you absolutely have to (which it really doesn't look like you do).
The best you can do, though, still isn't too bad.
var rows = ErrorTypesList
.Select(c => "\"" + string.Join("\",\"", c.RowNumber, c.ColumnNumber, c.ErrorMessage) + "\"");
File.WriteAllLines(path, rows);
I took the liberty of putting fields in quotes as well, you may or may not want that, but it's easy to fix that code to do what you do want. You might also want to add in some escape logic, pending what sorts of contents c.ErrorMessage might have.
You could also use string.Format if you're more comfortable with that, but it doesn't really make a difference here.
var rows = ErrorTypesList
.Select(c => string.Format("\"{0}\", \"{1}\", \"{2}\"", c.RowNumber, c.ColumnNumber, c.ErrorMessage));
It seems you want something like this:
string[] ErrorListArray = ErrorTypesList
.Select(e => string.Join(",", e.RowNumber, e.ColumnNumber, e.ErrorMessage))
.ToArray();
How do I check if a Guid value is inside a LIST of Structures?
public struct Info
{
public Guid EntityTypeID;
public String Name;
}
List<Info> InfoList = <function which populates the list of Struct>
...
var values = ctx.EntityValues.Where(v => v.EntityID == e.ID
&& InfoList.Contains(v.EntityTypeItemID)).ToList(); <=== problem here!
//or something like: InfoList[i].EntityTypeID.Contains(v.EntityTypeItemID)).ToList();
Thank you
I suspect you're looking for Any:
... InfoList.Any(x => x.EntityTypeID == v.EntityTypeItemID)
You can't use Contains, because you're looking for something which matches part of the item.
(I'd also strongly discourage using public fields and indeed having mutable structures at all, but that's a different matter.)
Another option would be to create a list of the GUIDs you're interested in:
var guids = InfoList.Select(x => x.EntityTypeID).ToList();
Then you can use:
... guids.Contains(v.EntityTypeItemID)
That may work where the previous code didn't, as it moves the extraction of the type ID out of the main query.
Let's say I have a table that I can query with EF + LINQ like this:
var results = dbContext.MyTable.Where(q => q.Flag = true);
Then, I know that if I want to limit the columns returned, I can just add a select in that line like this:
var results = dbContext.MyTable
.Select(model => new { model.column2, model.column4, model.column9 })
.Where(q => q.Flag == true);
The next step that I need to figure out, is how to select those columns dynamically. Said another way, I need to be able to select columns in a table withoutknowing what they are at compile time. So, for example, I need to be able to do something like this:
public IEnumerable<object> GetWhateverColumnsYouWant(List<string> columns = new List<string{ "column3", "column4", "column999"})
{
// automagical stuff goes here.
}
It is important to keep the returned record values strongly typed, meaning the values can't just be dumped into a list of strings. Is this something that can be accomplished with reflection? Or would generics fit this better? Honestly, I'm not sure where to start with this.
Thanks for any help.
I think you want some dynamic linq, Im no expert on this but i THINK it will go something like this
public static IEnumerable<object> GetWhateverColumnsYouWant(this IQueriable<T> query, List<string> columns = new List<string{ "column3", "column4", "column999"})
{
return query.Select("new (" + String.Join(", ", columns) + ")");
}
See scott Gu's blog here http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx and this question System.LINQ.Dynamic: Select(" new (...)") into a List<T> (or any other enumerable collection of <T>)
You could probably also do this by dynamically composing an expression tree of the columns youre wanting to select but this would be substantially more code to write.
I want to return a list of objects stored in a database using LINQ queries.
I tried the following
public BO.Hotel getHotels()
{
TripBagEntities db = new TripBagEntities();
var hotels = (from m in db.HotelEntities
where m.id < 10
select m).ToList().First();
return Mapper.ToHotelObject(hotels);
}
This returns only the first item in the list. How can I return the entire list?
Thanks in advance
Firstly, as per the comment, you should understand exactly what each line of your existing code does first. (You should also try to follow .NET naming conventions.) If you're guessing around which bit of your code does what, it would be a good idea to read a good tutorial geared towards the LINQ provider you're using (Entity Framework?).
We don't really know what Mapper.ToHotelObject does, or whether there's already a method for converting a whole sequence. This should work though:
public List<BO.Hotel> GetHotels()
{
// Note: you may want a using statement here...
TripBagEntities db = new TripBagEntities();
var hotels = db.HotelEntities
.Where(m => m.id < 10)
.AsEnumerable()
.Select(Mapper.ToHotelObject)
.ToList();
}
Or if the method group conversion doesn't work:
public List<BO.Hotel> GetHotels()
{
// Note: you may want a using statement here...
TripBagEntities db = new TripBagEntities();
var hotels = db.HotelEntities
.Where(m => m.id < 10)
.AsEnumerable()
.Select(m => Mapper.ToHotelObject(m))
.ToList();
}
Note that I've used "dot notation" for the whole query, as it makes life simpler when you're using things like AsEnumerable and ToList, and your query expression wasn't complicated anyway.
The AsEnumerable call "shifts" the query into LINQ to Objects, so that the query-to-SQL translation part doesn't need to try to convert Mapper.ToHotelObject into SQL, which I assume would fail.
You need to make your function return List<BO.Hotel> instead of a Hotel, and adjust your query and Mapper function accordingly.
public List<BO.Hotel> getHotels()
{
TripBagEntities db = new TripBagEntities();
return (from m in db.HotelEntities
where m.id < 10
select Mapper.ToHotelObject(m)).ToList();
}
I have some code that I know could be nicer if it's done in LINQ, but I don't know how the LINQ code would look like.
I have a collection of GoodsItems, in each of this Item there is a Collection of Comments, and some of these comments I want to filter out and turn into a single string line.
Here is the code:
//-- get all comments that is of type "GoodsDescription"
ICollection<FreeText> comments = new List<FreeText>();
foreach (DSV.Services.Shared.CDM.Shared.V2.GoodsItem goodsItem in shipmentInstructionMessage.ShipmentInstruction.ShipmentDetails.GoodsItems)
{
ICollection<DSV.Services.Shared.CDM.Shared.V2.FreeText> freeTexts = goodsItem.Comments.Where(c => c.Type.ToLower() == FREETEXT_TYPE_GOODSDESCRIPTION.ToLower()).ToList();
foreach (DSV.Services.Shared.CDM.Shared.V2.FreeText freeText in freeTexts)
comments.Add(FreeText.CreateFreeTextFromCDMFreeText(freeText));
}
//-- Turn this collection of comments into a single string line
StringBuilder sb = new StringBuilder();
foreach (FreeText comment in comments)
sb.Append(comment.ToString());
contents = sb.ToString();
First Foreach loops thru all goodsitems and for each goods item I get all comments where the Type of the comment is Equale to a defined value.
Then foreach of this comment that I get I create a new Object and add to a CommentsCollection.
And the last thing is that I loop thru this commentsColletion and create all it's data into a single string line.
There must be a nicer and smart way to do this with LINQ.
Thanks...
It looks like you could do this:
var comments = from goodsItem in shipmentInstructionMessage.ShipmentInstruction.ShipmentDetails.GoodsItems
from freeText in goodsItem.Comments.Where(c => string.Equals(c.Type, FREETEXT_TYPE_GOODSDESCRIPTION, StringComparison.InvariantCultureIgnoreCase))
select FreeText.CreateFreeTextFromCDMFreeText(freeText).ToString();
string contents = string.Join("", comments);
It's probably slightly more readable, if only because you've lost most of the types (although you could also have achieved this with implicitly typed local variables).
(I also changed how the string comparison on the comment type is done – I assume you were trying to achieve a case invariant comparison. You may want to use StringComparison.CurrentCultureIgnoreCase instead, depending on what the content of the comments is.)