how to get from one List on the bases of another List

Question

1.11/5 (2 votes)

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Hello 2 All...

i have 2 Generic Lists of the same type... FirstList Contains all the possible values getting from SupplierTable.. while the SecondList conatains some selected values of suppliers getting from ItemTable( i.e All those Suppliers for a specific item).....

Now i want to exract all values from FirstList which do not exist in the Secondlist????

what should i do for this???

Muhammad Tufail...

Posted 28-Jun-11 5:41am

Muhammad Tufail 1979

Updated 28-Jun-11 5:48am

v2

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Comments

Sergey Alexandrovich Kryukov 28-Jun-11 12:16pm

I don't know your code but have a feeling you do it too late. You could use proper SQL query to obtain the lists with the subsets of values you want, in first place.
The problem with list it trivial though.
--SA

Muhammad Tufail 1979 28-Jun-11 13:57pm

i have 2 quries one to bring all the suppliers in the firstList and the seconde query bring all the items with (suppliersList ... and this is my seconed list)

now i want to separate the values of second list from the first and remaing to show in a listbox.....

4 solutions

Solution 1

You can use Contains to do this. I know it seems counter-intuitive, but if you invert Contains, it becomes not contains. So, you could have code that looks like this:

C#

var myList = from c in firstList
    where !secondList.Contains(c.supplierId)
    select c;

Posted 28-Jun-11 5:49am

Pete O'Hanlon

Comments

Muhammad Tufail 1979 28-Jun-11 11:57am

Sorry Sir.... it doesnot working ..

it gives a problem that....... Contains method determine wether the value exists or not and return a boolean value...

i dont undersand but its not working plzzzzz.....

Pete O'Hanlon 28-Jun-11 12:14pm

That's right - it returns a boolean, but you are returning an IQueryable here. You can easily convert it to a list by evaluating myList.ToList(); or you could bracket the from bit like this:

var myList = (from c in firstList
where !secondList.Contains(c.supplierId)
select c).ToList();

Morl99 28-Jun-11 12:10pm

Use my method instead. If you want to preserve the original list, copy it beforehand.

Muhammad Tufail 1979 29-Jun-11 1:27am

i had tried all the following code but not got the right solution..

remainingSuppliers = from sp in suppliers where !it.Suppliers.Contains (sp.ID ) select sp;
var list = from sp in suppliers where !it.Suppliers.Contains(sp) select sp;
var list = (from sp in suppliers where !it.Suppliers.Contains(sp) select sp).ToList();

remainingSuppliers = suppliers.Except(it.Suppliers).ToList ();

foreach (Supplier ss in remainingSuppliers)
{
leftListBox.Items.Add(ss.Name);
}

Muhammad Tufail 1979 28-Jun-11 13:52pm

Now it does not give any error .... but it does not remove all those items which i want to remove from the firstlist......

first list conatain all those items which are in second list......

sorry still i didnt got the solution...

Pete O'Hanlon 28-Jun-11 14:10pm

Try swapping them over - the lists in my example are purely fictitious names - I hadn't realised that they matched the names you'd chosen.

Muhammad Tufail 1979 29-Jun-11 1:28am

i had tried all the following code but not got the right solution..

remainingSuppliers = from sp in suppliers where !it.Suppliers.Contains (sp.ID ) select sp;
var list = from sp in suppliers where !it.Suppliers.Contains(sp) select sp;
var list = (from sp in suppliers where !it.Suppliers.Contains(sp) select sp).ToList();

remainingSuppliers = suppliers.Except(it.Suppliers).ToList ();

foreach (Supplier ss in remainingSuppliers)
{
leftListBox.Items.Add(ss.Name);
}

Morl99 29-Jun-11 2:41am

Oh and don't get me wrong. I actually find your answer better than mine. But it is a lot harder to understand for somebody new to c#. I assume he has no idea of what is actually happening there. That's why he probably should use a simple for loop to iterate through the list. My Vote of 4 for this elegant, yet difficult solution.

Pete O'Hanlon 29-Jun-11 3:50am

I agree - I almost regret posting this solution; almost, but not quite.

Solution 2

Just iterate over the second List and remove the items you have there from the first list. Maybe like this:

List<T> firstList;
List<T> secondList;
foreach (T t in secondList){
  firstList.remove(t);
}

That should do the trick (If the items are truly equal). Of course you have to plugin your own types and variable names.

Now if the items are not really equal you need to check that for yourself. Try something like this

foreach (DataType supplierToRemove in secondList) {
  int supplierID = supplierToRemove.ID;
  DataType delete = null;
  foreach (DataType supplier in firstList){
    if(supplier.ID == supplierID){
      delete = supplier;
      break;
    }
  }
  if (delete != null)
    firstList.remove(delete);
}

Be aware that I don't know your code! You have to adapt this solution to your needs. If you do not have an ID, use your Primary Key of the Table instead.

Posted 28-Jun-11 5:50am

Morl99

Updated 28-Jun-11 21:20pm

v5

Comments

Muhammad Tufail 1979 28-Jun-11 13:53pm

Now it does not give any error .... but it does not remove all those items which i want to remove from the firstlist......

first list conatain all those items which are in second list......

sorry still i didnt got the solution...

Solution 4

i m very thankfull to all the codeproject team, and all those who provide me alot of help in solving the problems.. i got the solution of that problem and now i m going to improve myself futher more in this field...

thanx

Muhammad Tufail

Posted 1-Jul-11 20:57pm

Muhammad Tufail 1979

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Mohammad A Rahman · Accepted Answer · 2011-06-28T14:58:00

Solution 3

Could you please try following, it might help you to sort out the issue,

C#

var firstList = new List<string>() { "A", "B", "C" };
var secondList = new List<string>() { "A", "B" };
var resultList = firstList.Except(secondList);

Thanks :)

Posted 28-Jun-11 14:58pm

Mohammad A Rahman

Comments

Muhammad Tufail 1979 29-Jun-11 1:27am

i had tried all the following code but not got the right solution..

remainingSuppliers = from sp in suppliers where !it.Suppliers.Contains (sp.ID ) select sp;
var list = from sp in suppliers where !it.Suppliers.Contains(sp) select sp;
var list = (from sp in suppliers where !it.Suppliers.Contains(sp) select sp).ToList();

remainingSuppliers = suppliers.Except(it.Suppliers).ToList ();

foreach (Supplier ss in remainingSuppliers)
{
leftListBox.Items.Add(ss.Name);
}

Mohammad A Rahman 29-Jun-11 1:46am

Could you please give a example of Test data for suppliers and it.Suppliers and as well the output your getting. :)

Muhammad Tufail 1979 29-Jun-11 2:00am

i have 4 Suppliers in database ( tabel name is Suppliers) and
it.suppliers ( mean item.suppliers) this list contains 2 suppliers at the moment... i mean to say that ( every item has its own suppliers)....

now i want that to exclude these 2 suppliers from the suppliers List and the remaining suppliers should display in the listbox with the name of leftListBox.

Mohammad A Rahman 29-Jun-11 2:09am

I am assuming suppliers list contains {"A","B","C","D"}. Based on what you said, it.suppliers I guess it is a list with {"A","B"} then simply suppliers.Except(it.Suppliers) should give us {"C","D"}. In another case if it.suppliers is a single item (assumption) then suppliers.Except(List Of it.Suppliers). :)

Muhammad Tufail 1979 29-Jun-11 2:16am

yes exactly plz the first case is my case of problem plzzzzzz

Muhammad Tufail 1979 29-Jun-11 2:25am

But suppliers.Except(it.suppliers) does not give { "C", "D"} it gives again all 4 i.e { "A", "B","c","D}

Muhammad Tufail 1979 29-Jun-11 2:14am

if u dont mind plz so i can tell u some of detail .......

in database i have one table with the name of Items. 2nd table with the name of Suppliers . but both having many to many relationship. so there is a third table with the name of ItemsSuppliers ( contains just the pk of both tables)...

Now i have a Form to display all the particulars of items.. for the Suppliers i have two listBox ( leftListBox and rightListBox) leftListBox contain all the suppliers exist in database and there is a button to select from it and display it in the rightListBox and ( these should be the suppliers for that particular item and should also be saved with that item )......

Now when i want to retrive an item to display on a Form.. so i want that the supplier of this item should be display in rightListBox while the remaining Suppliers which are not the suppliers of that item should be display in the leftListBox.... ( i.e leftListbox contains all the suppliers but not those which are in the rightListBox)......

For this purpose i get all the suppliers from supplier table and want to remove all the suppliers of that particular item. which has been currently selected.....

the above code until i had tried.... do not remove the supplier of a particular item from the Supplier List..

it showes every time all ( 4 Suppliers inculing the item suppliers too) in the leftList box...
plz i m very Newer to .net plz i havent idea... just learning these techneques

thanx

Morl99 29-Jun-11 2:29am

I assume, that they are Not equal. What type are they? How do you identify the items as equal or not equal?

Mohammad A Rahman 29-Jun-11 2:33am

Following code absolutely give you one item which is "C",
var firstList = new List<string>() { "A", "B", "C" };
var secondList = new List<string>() { "A", "B" };
var resultList = firstList.Except(secondList);
I think after you get resultList you would need to repopulate the ListBox and when you repopulate the ListBox you must clear all the previous items from it. :)

Muhammad Tufail 1979 29-Jun-11 3:04am

Yes my brother its working very well.... it gives the desired result...
but i have both Lists of same type ( i.e Supplier (dataType))

Morl99 29-Jun-11 3:10am

The 2 lists of Mohammad also are of the same type (String). I will update my solution, maybe this will help.

Morl99 29-Jun-11 2:36am

Yeah that could also be the problem. If this is Windows Forms and not ASP, the thread opener could just print the contents of the Lists to the console to check (or better use the debugger)