C#: Count occurrences of a string in a list which is in another list using LINQ?

Question

I am trying to count occurrences of a string in dynamically added lists in a main list. This is the main list:

public static List<string>[] tables = new List<string>[30];

This is how I add items to it:

public static int takenTablesDayTotal;

public static void AddProductToTable()
{
    int tableNum = int.Parse(Console.ReadLine());

    if (tableNum < 1 || tableNum > 30) { throw new Exception(); }

    choiceName = Console.ReadLine();

    if (tables[tableNum] is null)
    {
        tables[tableNum] = new List<string>();
        takenTablesDayTotal++;
    }

    tables[tableNum].Add(choiceName);
}

And this is how I have tried to do the counting, but it doesn't seem to work right for some reason (starts at 1 and stops counting there when the required string is detected)

salesProductDayTotal = tables.Where(s => s != null && s.Contains("string")).Count();

I'm not sure how to make this work, so any help will be appreciated!

Thanks in advance!

Roberson Liou · Accepted Answer · 2020-05-17 12:00:42Z

4

You can use SelectMany to deliminate the two-nest structure. Then use Count to get what you want.

For example - count the daily apple sales number

List<string>[] tables = new List<string>[30];
tables[0] = new List<string>{
    "Apple", "Banana", "Cherry"
};
tables[1] = new List<string>{
    "Peach", "Apple", "Watermelon"
};
tables[2] = new List<string>{
    "Mango", "Grape", "Apple"
};

//the daily sales count of Apple.
var dailyAppleSalesCount = tables.Where(x => x != null)
        .SelectMany(s => s).Count(x => x == "Apple");

answered May 17, 2020 at 12:00

Roberson Liou

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Pac0 · Accepted Answer · 2020-05-17 11:58:25Z

3

You can use SelectMany to flatten the List<List<string>> into one large List<string>, and then count the products.

You don't need to use Contains, IMO ("Chicken soup" is probably a different product on the menu that "Spicy Chicken Soup"), so it simplifies the condition a bit.

salesProductDayTotal = tables
    .Where(t => t != null)
    .SelectMany(products => products)
    .Count(p => p == "string")

You could also use a GroupBy clause to do this calculations on all the products at once.

Explanation of your problem:

You were using the Count on the outer list, the list of tables. So you had just "one match" for each table that contains the product at least once.

answered May 17, 2020 at 11:58

Pac0

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