LESSON 166 OF 413 · PROJECTS: EVERYDAY PROGRAMS

Shopping Cart V6 - Group by Category in C#

Practice

Use a Dictionary to accumulate totals per category while looping over parallel arrays, then list the categories sorted by name.

You start with:

        string[] items = {"Apple", "Bread", "Shirt", "Banana", "Pants"};
        int[] prices = {2, 3, 25, 1, 40};
        string[] categories = {"Food", "Food", "Clothes", "Food", "Clothes"};

Build:

Clothes: $65
Food: $6

Rules:

Build a Dictionary totals that maps each category to the sum of the prices of its items.
Loop with an index. For each item, add its price to the total of categories[i]; a category you have not seen yet counts as 0.
Make one line per category, in the format "Category: $total", sorted alphabetically by category name (so Clothes comes before Food).
Join the lines with a newline "\n" into one string result, then print it with Console.WriteLine(result).

Use totals.ContainsKey(cat) ? totals[cat] : 0 as the starting value: reading a missing key with [] would throw.

Copy the keys into a List<string> and call Sort() on it, then loop over the sorted list.

        string[] items = {"Apple", "Bread", "Shirt", "Banana", "Pants"};
        int[] prices = {2, 3, 25, 1, 40};
        string[] categories = {"Food", "Food", "Clothes", "Food", "Clothes"};

        Dictionary<string, int> totals = new Dictionary<string, int>();
        for (int i = 0; i < items.Length; i++) {
            string cat = categories[i];
            totals[cat] = (totals.ContainsKey(cat) ? totals[cat] : 0) + prices[i];
        }
        List<string> lines = new List<string>();
        List<string> keys = new List<string>(totals.Keys);
        keys.Sort();
        foreach (string cat in keys) {
            lines.Add(cat + ": $" + totals[cat]);
        }
        string result = string.Join("\n", lines);
        Console.WriteLine(result);

STEP 1 OF 11

Guided

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Shopping Cart V6 - Group by Category in C#

Shopping Cart V6 in C#