Linq Query - get current month plus previous months - linq

Question

I need to build a Linq query that will show the results as follow:
Data:
Sales Month
----------------------
10 January
20 February
30 March
40 April
50 May
60 June
70 July
80 August
90 September
100 October
110 November
120 December
I need to get the results based on this scenario:
month x = month x + previous month
that will result in:
Sales Month
--------------------
10 January
30 February (30 = February 20 + January 10)
60 March (60 = March 30 + February 30)
100 April (100 = April 40 + March 60)
.........
Any help how to build this query ?
Thanks a lot!

Answer 1

Since you wanted it in LINQ...
void Main()
{
List<SaleCount> sales = new List<SaleCount>() {
new SaleCount() { Sales = 10, Month = 1 },
new SaleCount() { Sales = 20, Month = 2 },
new SaleCount() { Sales = 30, Month = 3 },
new SaleCount() { Sales = 40, Month = 4 },
...
};
var query = sales.Select ((s, i) => new
{
CurrentMonth = s.Month,
CurrentAndPreviousSales = s.Sales + sales.Take(i).Sum(sa => sa.Sales)
});
}
public class SaleCount
{
public int Sales { get; set; }
public int Month { get; set; }
}
...but in my opinion, this is a case where coming up with some fancy LINQ isn't going to be as clear as just writing out the code that the LINQ query is going to generate. This also doesn't scale. For example, including multiple years worth of data gets even more hairy when it wouldn't have to if it was just written out the "old fashioned way".

Answer 2

If you don't want add up all of the previous sales for each month, you will have to keep track of the total sales somehow. The Aggregate function works okay for this because we can build a list and use its last element as the current total for calculating the next element.
var sales = Enumerable.Range(1,12).Select(x => x * 10).ToList();
var sums = sales.Aggregate(new List<int>(), (list, sale) => list.Concat(new List<int>{list.LastOrDefault() + sale});