Set the logic of value usage - algorithm

Question

I want to implement a logic "If this_field is initialized, then: get its value, else: use the average value amongst all the initialized this_field in all listed objects instead". I know I can check the None in Foreach cycle, using specific field, but I want one function/interface/smth to use on all the fields (there are 50+ of them, so overloading might be too long, and too strict, in case I'll add more fields to my class).
For examle:
Foreach (City thiscity in Cities) {
thiscity.PolutionRoughEstimation = thiscity.PolutionData.MetalsPortion != None ?
thiscity.PolutionData.MetalsInAirPortion :
AverageKnown(Cities, Object.PolutionData.MetalsPortion) ;
}
Yet, I do not whant to write the overloading of AverageKnown for all parameters. I also don't want to write the same Foreach loop for each field. I just whant my system to use the average value of this group, whenever I have no data for it. There might be a way to write it once, but I just cannot figure it out.
Help me, please.

Answer 1

In C#, you can do this, by simply use Average method. See this:
static void Main(string[] args)
{
List<City> cities = new List<City>();
cities.Add(new City { Polution = 1, OtherField = 1 });
cities.Add(new City { Polution = 5, OtherField = 5 });
cities.Add(new City { OtherField = 2 });
double? ave = cities.Average(c => c.Polution);
}
public class City
{
public int? Polution;
public int? OtherField;
}
The value of ave is 3 not 2.
and so, it depends on the implementation of your programming language/lib.

Answer 2

Now I figured it out how to use reflections with expressions to fill the missing data
using System.Reflection;
public void FillGapInData(ref List<City> cities)
{
foreach (var city in cities)
{
Type t = city.GetType();
PropertyInfo[] parameteres = t.GetProperties();
foreach (var parameter in parameteres)
{
if (((double?)parameter.GetValue(city)).Equals(null))
{
double? a = cities
.Average(c => (double?)parameter.GetValue(c));
parameter.SetValue(city, a);
}
}
}
}
More accurate version, to ensure we do not spoil our string properties, and with -1 as an explicit mark for "missing data":
using System.Reflection;
public void FillGapInData(ref List<City> cities)
{
foreach (var city in cities)
{
Type t = city.GetType();
PropertyInfo[] parameteres = t.GetProperties();
foreach (var parameter in parameteres)
{
if (parameter.PropertyType == typeof(double?)) //check we have a number here
if ((((double?)parameter.GetValue(city)) == -1) || //check for -1 reserved mark
(((double?)parameter.GetValue(city)).Equals(null)))
{
double? a = cities
.Where(c => ( ((double?)(parameter.GetValue(c)) != -1)
&& !(((double?)(parameter.GetValue(c))).Equals(null)))) //I couldn't stop
.Average(c => (double?)(parameter.GetValue(c)));
parameter.SetValue(city, a);
}
}
}
}