Hello and welcome! Today, we're exploring practical data manipulation techniques in TypeScript. We'll utilize TypeScript arrays to represent our data streams and perform projection, filtering, and aggregation operations. Our operations will be neatly encapsulated within a TypeScript class for clean, structured code with built-in type annotations.

Data manipulation is akin to sculpting, but for data. We shape our dataset to derive the desired structure. TypeScript arrays with type annotations give us clarity and safety. Our manipulation operations will be part of a TypeScript class. Let's prepare our toolbox:

Our first stop is data projection, akin to capturing a photo of our desired features. Imagine we have data about people. If we're only interested in names and ages, we can project our data to focus solely on these details. We'll extend our DataStream class with a projectData method, leveraging TypeScript's type system:

The projectData method in the class creates a new instance that contains only the specified keys from each element in the original data array. It accepts an array of as input. The method iterates over each element in the data and constructs a new object, , for each element. Using for allows these objects to only include some properties of , making them optional. In the method, the loop assigns the value of each specified key to , ensuring that only desired fields are retained. The newly constructed , which consists of partially constructed objects, is then used to instantiate and return a new .