Dictionaries and Maps
Dictionaries (also known as Maps, Hash Maps, or Associative Arrays) are data structures that store data in key-value pairs. Unlike arrays which use numeric indices, dictionaries use unique keys to look up values.
1. Concept
- Key: A unique identifier for the data (e.g., "username", "id", 42).
- Value: The data associated with the key.
Think of a real-world dictionary: you look up a word (Key) to find its definition (Value).
2. Implementation in Languages
Python (Dictionary)
Python uses the dict type, defined with curly braces {}.
user = {
"name": "Alice",
"age": 30,
"is_admin": True
}JavaScript (Object & Map)
JavaScript traditionally uses Objects for key-value pairs, but modern JS also has a dedicated Map class.
Object:
let user = {
name: "Alice",
age: 30
};Map:
let inventory = new Map();
inventory.set("apple", 10);
inventory.set("banana", 5);Java (HashMap)
Java uses the Map interface, commonly implemented by HashMap.
import java.util.HashMap;
HashMap<String, Integer> scores = new HashMap<>();
scores.put("Alice", 95);
scores.put("Bob", 82);3. Common Operations
Accessing Values
- Python:
value = data["key"] - JavaScript:
value = data.keyordata["key"](Object),data.get("key")(Map) - Java:
value = map.get("key");
Adding/Updating
- Python:
data["new_key"] = "value" - JavaScript:
data.newKey = "value"(Object),map.set("key", "value")(Map) - Java:
map.put("key", "value");