LESSON 167 OF 414 · PROJECTS: EVERYDAY PROGRAMS

Shopping Cart V6 - Group by Category in Scala

Practice

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

You start with:

        val items = Array("Apple", "Bread", "Shirt", "Banana", "Pants")
        val prices = Array(2, 3, 25, 1, 40)
        val categories = Array("Food", "Food", "Clothes", "Food", "Clothes")

Build:

Clothes: $65
Food: $6

Rules:

Build a mutable map 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 println(result).

Use totals.getOrElse(cat, 0) + prices(i) to accumulate without checking for missing keys.

Use totals.keys.toSeq.sorted to get the keys in alphabetical order.

        val items = Array("Apple", "Bread", "Shirt", "Banana", "Pants")
        val prices = Array(2, 3, 25, 1, 40)
        val categories = Array("Food", "Food", "Clothes", "Food", "Clothes")

        val totals = scala.collection.mutable.Map[String, Int]()
        for (i <- items.indices) {
            val cat = categories(i)
            totals(cat) = totals.getOrElse(cat, 0) + prices(i)
        }
        val lines = scala.collection.mutable.ArrayBuffer[String]()
        val keys = totals.keys.toSeq.sorted
        for (cat <- keys) {
            lines += cat + ": $" + totals(cat)
        }
        val result = lines.mkString("\n")
        println(result)

STEP 1 OF 10

Guided

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Shopping Cart V6 - Group by Category in Scala

Shopping Cart V6 in Scala