get sum from list of objects in linq C# - linq

Question

I have list of objects as described below:
List<Maths> mObjs = new List<Maths>();
mObjs.Add(new Maths{ Name = "Jack", M1 = 10, M2 = 5, M3 = 0, M4 = 2, M5 =1 });
mObjs.Add(new Maths { Name = "Jill", M1 = 2, M2 = 3, M3 = 4, M4 = 1, M5 = 0 });
mObjs.Add(new Maths { Name = "Michel", M1 = 12, M2 = 15, M3 = 10, M4 = 12, M5 = 11 });
Now I need to calculated the total aggregated value for all three people.
I need to get the below results, probably a new other class
List<Results> mRes = new List<Results>();
public class Results{
public string Name { get; set; }
public int TotalValue { get; set; }
}
mRes.Name = "M1"
mRes.TotalValue = 24;
mRes.Name = "M2"
mRes.TotalValue = 23;
mRes.Name = "M3"
mRes.TotalValue = 14;
mRes.Name = "M4"
mRes.TotalValue = 15;
mRes.Name = "M5"
mRes.TotalValue = 12;
How can I get this data from mObjs using linq query? I know we can do it using for, but want to know if there are any better ways to get this using linq query because that reduces lines of code and I have similar requirements in many other places and dont want to write number of foreach or fors every time.

Answer 1

You can use a pre selection list to list both the name and the field to select
var lookups = new Dictionary<string,Func<Maths,int>> {
{"M1", x => x.M1 },
{"M2", x => x.M2 },
{"M3", x => x.M3 },
{"M4", x => x.M4 },
{"M5", x => x.M5 },
};
Then you can simply do
var mRes = dlookups.Select(x => new Results {
Name= x.Key,
TotalValue = mObjs.Sum(x.Value)
}).ToList();
BEGIN UPDATED*
In response to comments
The lambda expression is just a function from your source class to an int.
For example
class Sub1 {
string M3 {get;set;}
int M4 {get;set;}
}
class Math2 {
string Name {get;set;}
string M1 {get;set;}
string M2 {get;set;}
Sub1 Sub {get;set;}
}
var lookups = new Dictionary<string,Func<Math2,int>> {
{ "M1", x => int.Parse(x.M1) },
{ "M2", x => int.Parse(x.M2) },
{ "M3", x => int.Parse(x.Sub.M3) },
{ "M4", x => int.Parse(x.Sub.M4} }
};
Or if you want to put a little error checking in, you can either use functions or embed the code.
int GetInt(string source) {
if (source == null) return 0;
int result;
return int.TryParse(source, out result) ? result : 0;
}
var lookups = new Dictionary<string,Func<Math2,int>> {
{ "M1", x => {
int result;
return x == null ? 0 : (int.TryParse(x,out result) ? result : 0);
},
{ "M2", x => GetInt(x) },
{ "M3", x => x.Sub == null ? 0 : GetInt(x.Sub.M3) },
{ "M4", x => x.Sub == null ? 0 : x.Sub.M4}
};
END UPDATED
If you want to go further you could use reflection to build the lookups dictionary.
Here is a helper function that will generate the lookups for all Integer properties of a class.
public Dictionary<string,Func<T,int>> GenerateLookups<T>() where T: class {
// This just looks for int properties, you could add your own filter
var properties = typeof(T).GetProperties().Where(pi => pi.PropertyType == typeof(int));
var parameter = Expression.Parameter(typeof(T));
return properties.Select(x => new {
Key = x.Name,
Value = Expression.Lambda<Func<T,int>>(Expression.Property(parameter,x),parameter).Compile()
}).ToDictionary (x => x.Key, x => x.Value);
}
Now you can just do:
var mRes=GenerateLookups<Maths>().Select( x => new Results
{
Name = x.Key,
TotalValue = mObjs.Sum(x.Value)
}).ToList();

Answer 2

Not very smart but efficient and readable:
int m1Total= 0;
int m2Total= 0;
int m3Total= 0;
int m4Total= 0;
int m5Total= 0;
foreach(Maths m in mObjs)
{
m1Total += m.M1;
m2Total += m.M2;
m3Total += m.M3;
m4Total += m.M4;
m5Total += m.M5;
}
List<Results> mRes = new List<Results>
{
new Results{ Name = "M1", TotalValue = m1Total },
new Results{ Name = "M2", TotalValue = m2Total },
new Results{ Name = "M3", TotalValue = m3Total },
new Results{ Name = "M4", TotalValue = m4Total },
new Results{ Name = "M5", TotalValue = m5Total },
};
Result:
Name: "M1" TotalValue: 24
Name: "M2" TotalValue: 23
Name: "M3" TotalValue: 14
Name: "M4" TotalValue: 15
Name: "M5" TotalValue: 12
Edit: since you've explicitly asked for LINQ, if the properties are always these five i don't see why you need to use LINQ at all. If the number can change i would use a different structure.
You could for example use
a single List<Measurement> instead of multiple properties where Measurement is another class that stores the name and the value or you could use
a Dictionary<string, int> for efficient lookup.

Answer 3

You can try out some thing like this :
mRes.Add(new Results() { Name = "M1", TotalValue = mObjs.Sum(x => x.M1) });
To programmatically iterate through all the class properties, you might need to employ reflection.