linq query to group the items

var sales = _salesService.GetSales(parameters)

The list is something like

var listSales = new List<SalesData>();
listSales .Add(new SalesData
{
    Name = "Apple",
    Quantity = 1000
});
listSales .Add(new SalesData
{
    Name = "Banana",
    Quantity = 2000
});
listSales .Add(new SalesData
{
    Name = "Peach",
    Quantity = 1
});
listSales .Add(new SalesData
{
    Name = "Mango",
    Quantity = 1
});

I want to write a linq query so that I can group the 'Name' as 'Others' if the quantity is less than 1 percent of the total quantity.

So result of the query should be something like

Apple  56
Banana 23
Others 2  -- ( peach's quantity less than than 1% + Mango Quantity less than 1%)

Solution

Well, it sounds like first you need to know the total quantity. That's easy enough:

var total = listSales.Sum(entry => entry.Quantity);

Then you need to work out the cutoff point, which is 1% of it:

var cutoff = total / 100;

For the grouping and summing, I'd probably go in three steps:

Transform the original list into a sequence with entries of "Others"
Group entries by name
Sum per group

So the overall code would be:

var total = listSales.Sum(entry => entry.Quantity);
// TODO: Work out whether you want the cutoff to be exclusive or not.
var cutoff = total / 100;
var results = listSales.Select(entry => entry.Quantity >= cutoff ?
                                            entry :
                                            new SalesData { 
                                                Name = "Others",
                                                Quantity = entry.Quantity
                                            })
                       .GroupBy(entry => entry.Name, entry => entry.Quantity)
                       .Select(group => new { Name = group.Key,
                                              Total = group.Sum() });

You can combine the "group and select" operations, but personally I find the above simpler to read.