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Problem with delegate within foreach

The picture shown below represents my data. Data that I have and the expected result at the end:

The logic being, that for every date in the list of dates, find the associated price tuple where the effective date is less than or equal to the date and is the max date.

The structure of Price is shown below.

public class Price
public int PriceId { get; set; }

public DateTime EffectiveDate { get; set; }

public double PriceAmount { get; set; }

public DateTime CreatedOn { get; set; }

I have a static method that gets me the data that I need
static List<Price> GetPrices()
return new List<Price>()
new Price()
PriceId = 1, EffectiveDate = new DateTime(2012,1,1),
PriceAmount = 100, CreatedOn = new DateTime(2012,1,1)
new Price()
PriceId = 2, EffectiveDate = new DateTime(2012,1,1),
PriceAmount = 200, CreatedOn = new DateTime(2012,1,1)
new Price()
PriceId = 3, EffectiveDate = new DateTime(2012,1,2),
PriceAmount = 300, CreatedOn = new DateTime(2012,1,2)
new Price()
PriceId = 4, EffectiveDate = new DateTime(2012,1,3),
PriceAmount = 400, CreatedOn = new DateTime(2012,1,3)
new Price()
PriceId = 5, EffectiveDate = new DateTime(2012,1,4),
PriceAmount = 500, CreatedOn = new DateTime(2012,1,4)
new Price()
PriceId = 6, EffectiveDate = new DateTime(2012,1,5),
PriceAmount = 600, CreatedOn = new DateTime(2012,1,5)
new Price()
PriceId = 7, EffectiveDate = new DateTime(2012,1,16),
PriceAmount = 700, CreatedOn = new DateTime(2012,1,16)
new Price()
PriceId = 8, EffectiveDate = new DateTime(2012,1,27),
PriceAmount = 800, CreatedOn = new DateTime(2012,1,27)
new Price()
PriceId = 9, EffectiveDate = new DateTime(2012,1,28),
PriceAmount = 900, CreatedOn = new DateTime(2012,1,28)

This is the original code that I wrote to get me the information that I needed:

// This represents your List of dates
var listOfDates = new List<DateTime>()
new DateTime(2012,1,2),
new DateTime(2012,1,10),
new DateTime(2012,1,15),
new DateTime(2012,1,27)

// This represents your prices
var prices = GetPrices();

// Initialise the expected result set
var expectedResultSet = new List<Price>();

// Get your expected result set
listOfDates.ForEach(date =>
// In each date, find the price that you're after
var price = prices
.Where(p => p.EffectiveDate <= date)
.OrderByDescending(result => result.EffectiveDate)

if(price != null)
// Fix the Date
price.EffectiveDate = date;

// Add it to the expected result

// Print the Result

If you check the output, this does NOT give you the result you were expecting!!!
Now to get the result you're after, you'll need to iterate through the list in a different manner:

(This is just one option ... )

// Get Dates and Prices
listOfDates = GetListOfDates();
prices = GetPrices();

// Step A: Get a Tuple of Date & Price
List<Tuple<DateTime, Price>> datesWithAssociatedPrice;
datesWithAssociatedPrice = listOfDates
// Step 1: Select the Requested Date and Price(S)
// where the Price's Effective Date <= the date (from range)
// [One Date .. Many Prices]
.Select(eachDate => new
RequestedDate = eachDate,
AssociatedPrices = prices.Where(p => p.EffectiveDate <= eachDate)

// Step 2: Now iterate through the list of Date, List & in each tuple,
// find the first instance of Price with the Max Effective date
.Select(dateAndPrice => new
RequestedDate = dateAndPrice.RequestedDate,
AssociatedPrice = dateAndPrice
.First(price => price.EffectiveDate ==
dateAndPrice.AssociatedPrices.Max(item => item.EffectiveDate))

// Step 3: Now get the data you need as a List<Tuple<DateTime, Price>> tuple
.Select(tuple =>
new Tuple<DateTime, Price>(tuple.RequestedDate,

// Print using an extension method :)

And now the result is what is expected.

The complete source is available here:



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