Develop Reference

Retrieve value from a sorted dictionary with the help of ke in C#

I have a Dictionary, which has a hash table, that is, keys are not sorted.
Conflicts oConflicts = oClash.Conflicts;
Dictionary<string, string> dConflicts = new Dictionary<string, string>();
Conflict oConflict;
for (int iLoopC = 1; iLoopC <= oConflicts.Count; iLoopC++)
{
oConflict = oConflicts.Item(iLoopC);
if (Math.Abs(oConflict.Value) < 3)
{
dConflicts.Add(oConflict.Value.ToString(), oConflict.SecondProduct.ToString());
}
}
I have sorted the dictionary by LINQ:
var sortedDict = dConflicts.OrderBy(x => x.Value).ToDictionary(x => x.Key, x => x.Value);
I am new to this. Could someone help me with how to get the value stored in sortedDict using the particular key value? Like the last value using count the array elements.

This seems that you are only using a Dictionary just to be sure not Adding duplicates, pretty overkill, but hey...
var searchedLastElement = dConflicts.OrderBy(x => x.Value).LastOrDefault().Value;
yod didn't need the sorted list to be cast again to dictionary only to retrieve the last element

How to store the result of a linq query in a KeyDictionary variable

So I have a collection of objects who have multiple properties, two of these are groupname and personname. Now I need to count in the collection how many of each object belong to a certain group and person. So in other words, I need to group by groupname, then personname and then count how many objects have this combination. First I created this
public MultiKeyDictionary<string, string, int> GetPersonsPerGroup(IEnumerable<Home> homes ,List<string> gr, List<string> na)
{
List<string> groups = gr;
groups.Add("");
List<string> names = na;
names.Add("");
List<Home> Filtered = homes.ToList();
Filtered.ForEach(h => h.RemoveNull());
var result = new MultiKeyDictionary<string, string, int>();
int counter1 = 0;
foreach (var g in groups)
{
int counter2 = 0;
foreach (var n in names)
{
int counter3 = 0;
foreach (Home h in Filtered)
{
if (h.GroupName == g && h.PersonName == n)
{
counter3++;
if (counter3 > 100)
break;
}
}
if (counter3 > 0)
{
result.Add(g,n,counter3);
}
counter2++;
}
counter1++;
}
Which may look good, but the problem is that the "home" parameter can contain more than 10000 objects, with more than 1500 unique names and around 200 unique groups. Which causes this to iterate like a billion times really slowing my program down. So I need an other way of handling this. Which made me decide to try using linq. Which led to this creation:
var newList = Filtered.GroupBy(x => new { x.GroupName, x.PersonName })
.Select(y => (MultiKeyDictionary<string, string, int>)result.Add(y.Key.GroupName, y.Key.PersonName, y.ToList().Count));
Which gives an error "Cannot convert type 'void' to 'MultiKeyDictionary<string,string,int>' and I have no idea how to solve it. How can I make it so that the result of this query gets stored all in one MultikeyDictionary without having to iterate over each possible combination and counting all of them.
Some information:
MultiKeyDictionary is a class I defined (something I found on here actually), it's just a normal dictionary but with two keys assosiated to one value.
The RemoveNull() method on the Home object makes sure that all the properties of the Home object are not null. If it is the case the value gets sets to something not null ("null", basic date, 0, ...).
The parameters are:
homes = a list of Home objects received from an other class
gr = a list of all the unique groups in the list of homes
na = a list of all the unique names in the list of homes
The same name can occur on different groups
Hopefully someone can help me get further!
Thanks in advance!

Select must return something. You are not returning but only adding to an existing list. Do this instead:
var newList = Filtered.GroupBy(x => new { x.GroupName, x.PersonName }):
var result = new MultiKeyDictionary<string, string, int>);
foreach(var y in newList)
{
result.Add(y.Key.GroupName, y.Key.PersonName, y.ToList().Count));
}
The reason you are getting error below:
"Cannot convert type 'void' to 'MultiKeyDictionary'
is because you are trying to cast the returned value from Add which is void to MultiKeyDictionary<string,string,int> which clearly cannot be done.

If MultiKeyDictionary requires the two keys to match in order to find a result, then you might want to just use a regular Dictionary with a Tuple as a composite type. C# 7 has features that make this pretty easy:
public Dictionary<(string, string), int> GetPersonsPerGroup(IEnumerable<Home> homes ,List<string> gr, List<string> na)
{
return Filtered.GroupBy(x => (x.GroupName, x.PersonName))
.ToDictionary(g => g.Key, g => g.Count);
}
You can even associate optional compile-time names with your tuple's values, by declaring it like this: Dictionary<(string groupName, string personName), int>.

Your grouping key anonymous object should work fine as a standard Dictionary key, so no reason to create a new type of Dictionary unless it offers special access via single keys, so just convert the grouping to a standard Dictionary:
var result = Filtered.GroupBy(f => new { f.GroupName, f.PersonName })
.ToDictionary(fg => fg.Key, fg => fg.Count());

Show only columns from an string array

I have a Table in my Entities with 370 columns ! Furthermore i have a string Array which is not known before runtime (comes from a website).
e.g.:
string [] columns = {"column1", "column2", "column3"}
How can i fire a linq to my entities which gives me only the result with the giving columns?
I searched for hours, but don`t suceed till now - any suggestions?

This is not something that you can do with Linq-to-Entities. You need to be able to declare the columns in your code.
A better approach would be to create the query in Sql using the column names in your array, and use something like Dapper to map the results to your objects.

You could instantiate an ExpandoObject in your Delegate and use Reflection to get the columns specified in the incoming array.
The following:
List<IDictionary<String, Object>> List = Context.Row_Type.Select(delegate(Row_Type Row) {
IDictionary<String, Object> Out = new ExpandoObject() as IDictionary<String, Object>;
PropertyInfo[] PIs = Row.GetType().GetProperties();
foreach(PropertyInfo PI in PIs) {
if(PI.GetIndexParameters().Length == 0) {
Out.Add(PI.Name, PI.GetValue(Row));
}
}
return Out;
}).ToList();
Will return a List < IDictionary< String, Object>> with all the properties, to return the desired columns just discriminate by PI.Name:
if(PI.Name == "Desired column"){ // Or Array index
// Add to Out:
Out.Add( PI.Name, PI.GetValue(Row) )
}

I'm guessing you don't really want to return a class with unknown column names. Would a dictionary of column names and values work for you? Your query would still have to retrieve all of the columns, but you can only return the ones you care about.
string [] columns = {"column1", "column2", "column3"}
var entity = GetEntity();
var dictionary = columns.ToDictionary(c => c, c => entity.GetType().GetProperty(c).GetValue(entity));
Or, if you have a collection...
var entities = GetEntities();
var results = entities
.Select(e => columns.ToDictionary(c => c, c => e.GetType().GetProperty(c).GetValue(e)));

Dapper: How to read into list of Dictionary from query?

Dapper provides lots of ways mapping data into list of dynamic objects. However in some case I'd like to read data to list of Dictionary.
The SQL may looks like:
"SELECT * FROM tb_User"
As tb_User may change outside, I don't know what columns will return in result. So I can write some code like this:
var listOfDict = conn.QueryAsDictionary(sql);
foreach (var dict in listOfDict) {
if (dict.Contains("anyColumn")) {
// do right thing...
}
}
Is there any built-in methods for Dapper to do this conversion?

You can cast each row as IDictionary:
var row = (IDictionary<string, object>)conn.Query("select foo = 1, bar = 'bar'").First();
Assert.That(row["foo"], Is.EqualTo(1));
Assert.That(row["bar"], Is.EqualTo("bar"));

You could use the Cast extension method from System.Linq
IEnumerable<IDictionary<string, object>> rows;
rows = connection.Query(sqlRequest).Cast<IDictionary<string, object>>();
foreach (var row in rows)
{
var columnValue = row['columnName']; // returns the value of the column name
}

You can just assign aliases to your query so that it matches the Key and Value properties of a KeyValuePair and then use the .ToDictionary method like this:
var dict = db.Query<KeyValuePair<string, int>>(#"
SELECT COMMUNITY_TYPE As Key, COUNT(*) AS Value
FROM SNCOMM.COMMUNITY
GROUP BY COMMUNITY_TYPE")
.ToDictionary(x => x.Key, x => x.Value);
Now you have a Dictionary<string, int> without any manual converting.

Find the index position of duplicate entries in a comma separated string

My problem just got more complicated than I thought and I've just wiped out my original question... So I'll probably post multiple questions depending on how I get on with this.
Anyway, back to the problem. I need to find the index position of duplicate entries in string that contains csv data. For example,
FirstName,LastName,Address,Address,Address,City,PostCode,PostCode, Country
As you can see the Address is duplicated and I need to find out the index of each duplicates assuming first index position starts at 0.
If you have a better suggestion on how to do this, let me know, but assuming it can be done, could we maybe have with a dicitionary>?
So if I had to code this, you would have:
duplicateIndexList.Add(2);
duplicateIndexList.Add(3);
duplicateIndexList.Add(4);
myDuplicateList.Add("Address", duplicateIndexList);
duplicateIndexList.Add(6);
duplicateIndexList.Add(7);
myDuplicateList.Add("PostCode", duplicateIndexList);
Obviously I don't want to do this but is it possible to achieve the above using Linq to do this? I could probably write a function that does this, but I love seeing how things can be done with Linq.
In case you're curious as to why I want to do this? Well, in short, I have an xml definition which is used to map csv fields to a database field and I want to first find out if there are any duplicate columns, I then want to append the relevant values from the actual csv row i.e. Address = Address(2) + Address(3) + Address(4), PostCode = PostCode(6) + PostCode(7)
The next part will be how to remove all the relevant values from the csv string defined above based on the indexes found once I have appended their actual values, but that will be the next part.
Thanks.
T.
UPDATE:
Here is the function that does what I want but as I said, linq would be nice. Note that in this function I'm using a list instead of the comma separated string as I haven't converted that list yet to a csv string.
Dictionary<string, List<int>> duplicateEntries = new Dictionary<string, List<int>>();
int indexPosition = 0;
foreach (string fieldName in Mapping.Select(m=>m.FieldName))
{
string key = fieldName.ToUpper();
if (duplicateEntries.ContainsKey(key))
{
List<int> indexes = duplicateEntries[fieldName];
indexes.Add(indexPosition);
duplicateEntries[key] = indexes;
indexes = null;
}
else
{
duplicateEntries.Add(key, new List<int>() { indexPosition });
}
indexPosition += 1;
}
Maybe this will help clarify what I'm trying to achieve.

You need to do the following:
Use .Select on the resulting array to project a new IEnumerable of objects that contains the index of the item in the array along with the value.
Use either ToLookup or GroupBy and ToDictionary to group the results by column value.
Seems like an ILookup<string, int> would be appropriate here:
var lookup = columnArray
.Select((c, i) => new { Value = c, Index = i })
.ToLookup(o => o.Value, o => o.Index);
List<int> addressIndexes = lookup["Address"].ToList(); // 2, 3, 4
Or if you wanted to create a Dictionary<string, List<int>>:
Dictionary<string, List<int>> dictionary = columnArray
.Select((c, i) => new { Value = c, Index = i })
.GroupBy(o => o.Value, o => o.Index)
.ToDictionary(grp => grp.Key, grp => grp.ToList());
List<int> addressIndexes = dictionary["Address"]; // 2, 3, 4
Edit
(in response to updated question)
This should work:
Dictionary<string, List<int>> duplicateEntries = Mapping
.Select((m, i) => new { Value = m.FieldName, Index = i })
.GroupBy(o => o.Value, o => o.Index)
.ToDictionary(grp => grp.Key, grp => grp.ToList());

You could do something like :
int count = 0;
var numbered_collection =
from line in File.ReadAllLines("your_csv_name.csv").Skip(1)
let parts = line.Split(',')
select new CarClass()
{
Id = count++,
First_Field = parts[0],
Second_Field = parts[1], // rinse and repeat
};
This gives you Id's per item. (and also skip the first line which has the header). You could put it in a method if you want to automatically map the names from the first csv line to the fields).
From there, you can do:
var duplicates = (from items in numbered_collection
group items by items.First_Field into g
select g)
.Where(g => g.Count() > 1);
Now you have all the groups where you actually have duplicates, and you can just get the 'Id' from the object to know which one is the duplicated.