Develop Reference

C# Count occurrences in List Dynamically

I have a List<String> Fruits that stores a list of fruits the user enters.
For example Fruits = {"Apple", "Banana", "Apple", "Orange"}
I would like to count the number of occurrences of each fruit.
How do I go about this?
I come from a python background, and to solve this I would use dictionary. Any hints would be greatly appreciated

You may GroupBy the friuit name and take count of each group:
Fruits.GroupBy(x => x).Select(x => new {Name = x.Key, Count = x.Count()});
Live Demo

Utilise GroupBy followed with ToDictionary:
Dictionary<string, int> result = fruits.GroupBy(x => x)
.ToDictionary(x => x.Key, x => x.Count());

Get sum of the value from list using linq?

I am trying to get the sum of the value from list of list using linq ?my data is as below code
List<List<string>> allData = new List<List<string>>();
using (StreamReader reader = new StreamReader(path))
{
while (!reader.EndOfStream)
{
List<string> dataList;
dataList = reader.ReadLine().Split('|').ToList();
allData.Add(dataList);
}
}
which gives me data in allData as below
allData-->[0]-->[0]-'name1'
[1]-'sub'
[2]-'12'
[1]-->[0]-'name2'
[1]-'sub'
[2]-'15'
[2]-->[0]-'name1'
[1]-'sub2'
[2]-'15'
//and so on ....
i have applied group by that gives me grouping by the name but i am not able to figure out how to get the sum of the marks for each name ?
var grouped = allData.GroupBy(x => x[0]);
after this i get all matching name grouped into one but now how to get sum of the marks for that group ? any help would be great ?
Output should be name1=27 and name2=15 and so on.

Not sure if you want to get the sum of every group or the total. If it's the total then this should do the trick
var sum = allData.Sum(x => Int32.Parse(x[2]));
If it's per key then try the following
var all = allData
.GroupBy(x => x[0])
.Select(x => x.Sum(y => Int32.Parse(y[2]));

var grouped = allData.GroupBy(x => x[0])
.Select(g => new
{
Name = g.Key,
Sum = g.Sum(x => int.Parse(x[2]))
});
It will return an anonymous type instance for each group, with two properties: Name with your grouping key and Sum with sum of marks.

Sticking as much as possible to the LINQ query language:
var grouped = from d in allData
group d by i[0] into g
select new
{
Name = g.Key,
Sum = g.Sum(i => int.Parse(i[2]))
};

This will give you parallel List with each name and the count of how many times each name occurs.
var names = grouped.Select(s => s.Key).ToList();
var nameCount = grouped.Select(s => s.Count()).ToList();
Also... you may want to add this when assigning alldata to grouped. I use this to get a List from greatest to least amount of occurrences.
var grouped = allData.GroupBy(x => x[0]).OrderByDescending(i => i.Count());

How do i sum a list of items by code(or any field)?

I have an object that has a list of another object in it. i.e Object1 contains List<Object2>.
Assuming this is the definition of object 2:
public class Object2
{
string code,
string name,
decimal amount
}
I want to be a able to make a list2 from the list whose value will contain what something similar to what a select name, code, sum(amount) group by code kinda statement could have given me
this is what i did but it didnt contain what i needed on passing through.
var newlist = obj2List.GroupBy(x => x.code)
.Select(g => new { Amount = g.Sum(x => x.amount) });
I want code and name in the new list just like the sql statement above.

You're almost there:
var newlist = obj2List.GroupBy(x => x.code)
.Select(g => new
{
Code = g.First().code,
Name = g.First().name,
Amount = g.Sum(x => x.amount)
});
This groups the items by code and creates an anonymous object for each group, taking the code and name of first item of the group. (I assume that all items with the same code also have the same name.)

If you are grouping by code and not by name you'd have to choose something for name from the list, perhaps with First() or Last() or something.
var newlist = obj2List.GroupBy(x => x.code).Select(g => new {
Code = g.Key,
Name = g.First().name,
Amount = g.Sum(x => x.amount)
});

var query = Object1.Obj2List
.GroupBy(obj2 => obj2.code)
.Select(g => new {
Names = string.Join(",", g.Select(obj2.name)),
Code = g.Key,
Amount = g.Sum(obj2 => obj2.Amount)
});
Since you group by code only you need to aggregate the name also in some way. I have used string.Join to create a string like "Name1,Name2,Name3" for each code-group.
Now you could consume the query for example with a foreach:
foreach(var x in query)
{
Console.WriteLine("Code: {0} Names: {1} Amount: {2}"
, x.Code, x.Names, x.Amount);
}

Instead of using the LINQ Extension Methods .GroupBy() and .Select() you could also use a pure LINQ statement which is way easier to read if you come from a SQL Background.
var ls = new List<Object2>();
var newLs = from obj in ls
group obj by obj.code into codeGroup
select new { code = codeGroup.Key, amount = codeGroup.Sum(s => s.amount) };

Get distinct items from a list

I have a list of objects with three integer properties. How can I get the distinct values of first integer property from my list?

This should work,
List<int> result = YourListObject.Select(o => o.FirstInteger).Distinct().ToList();

Try:
var g = collection.Select(i => i.Property1).Distinct();
Could you post some source code so that we can give you a better example?
EDIT:
In my example, I have a collection collection which contains numerous instances of your class. I'm then selecting Property1 from each class, filtering to the distinct values of that property.

I have found this useful and working fine for me for strings.
var distinctNames = (from d in YourList select d).Distinct();
Hope this is useful for some one like me searching for details in SO.

Example of a more complex distinct'ing....
licenseLookupItems = tmpList
.GroupBy(x => new {x.LicenseNumber, x.Name, x.Location, x.Active, x.Archived})
.Select(p => p.FirstOrDefault())
.Select(p => new LicenseNumberLookupItem
{
LicenseNumber = p.LicenseNumber,
Name = p.Name,
Location = p.Location,
Active = p.Active,
Archived = p.Archived
})
.ToList();

LINQ - Need help with a statement/ scenario

Here's the scenario:
Given a List of Outputs each associated with an integer based GroupNumber. For each distinct GroupNumber within the List of Outputs starting with the lowest GroupNumber (1). Cycle through that distinct group number set and execute a validation method.
Basically, starting from the lowest to highest group number, validate a set of outputs first before validating a higher groupnumber set.
Thanks,
Matt

There's almost too many ways to solve this:
Here's one for a void Validate method.
source
.GroupBy(x => x.GroupNumber)
.OrderBy(g => g.Key)
.ToList()
.ForEach(g => Validate(g));
Here's one for a bool Validate method.
var results = source
.GroupBy(x => x.GroupNumber)
.OrderBy(g => g.Key)
.Select(g => new
{
GroupNumber = g.Key,
Result = Validate(g),
Items = g.ToList()
})
.ToList();

If you need them as groups:
var qry = source.GroupBy(x=>x.GroupNumber).OrderBy(grp => grp.Key);
foreach(var grp in qry) {
Console.WriteLine(grp.Key);
foreach(var item in grp) {...}
}
If you just need them ordered as though they are grouped:
var qry = source.OrderBy(x=>x.GroupNumber);