hash maps

average_speed/src/main.rs

@@ -0,0 +1,80 @@
+fn main() {
+    use std::collections::HashMap;
+
+    // initialize a hash map of runners to store their average lap timings
+    let mut runners = HashMap::new();
+
+    let joe = "Joe".to_string();
+    let jill = "Jill".to_string();
+    let jane = "Jane".to_string();
+    let jack = "Jack".to_string();
+
+    // insert joe and set his average to 10
+    runners.insert(joe.clone(), 10);
+    println!("DEBUG: there's only Joe");
+    println!("\tthe current values are:\n\t{runners:?}");
+
+    // insert other runners and set their default values
+    runners.entry(jill.clone()).or_insert(5);
+    runners.entry(jane.clone()).or_insert(5);
+    runners.entry(jack.clone()).or_insert(5);
+    println!("\nDEBUG: we initialized Jill, Jane and Jack with 5 minutes per lap");
+    println!("\tthe current values are:\n\t{runners:?}");
+
+    // hard update jill's average to another value
+    println!("\nDEBUG: hard setting Jill's value to 20");
+    println!("\tJill's average before: {:?}", runners.get(&jill).unwrap());
+    runners.insert(jill.clone(), 20);
+    println!("\tJill's average after: {:?}", runners.get(&jill).unwrap());
+
+    // update current values based on old values
+    println!(
+        "\nDEBUG: runners have completed one lap
+       their timings are:
+       \tJill: 4
+       \tJack: 10
+       \tJane: 8
+       \tJoe: 9"
+    );
+    println!("\nDEBUG: updating their values...");
+    println!("\tvalues before updating:\n\t{runners:?}");
+
+    // can be improved using hash maps
+    let val = vec![4, 10, 8, 9];
+    let names = ["Jill", "Jack", "Jane", "Joe"];
+
+    let mut count = 0;
+
+    for n in names {
+        let tmp = n.to_string();
+        let updater = runners.entry(tmp.clone()).or_insert(0);
+        *updater += val[count];
+        *updater /= 2;
+        count += 1;
+    }
+
+    println!("\n\tvalues after updating:\n\t{runners:?}");
+}
+
+/* figuring out how to update values
+
+println!("Jill's average before: {:?}", runners.get(&jill).unwrap());
+
+let curr_value = runners.get(&jill).unwrap();
+println!("\t{curr_value}");
+
+let new_value = 4;
+println!("\t{new_value}");
+
+let final_value = (curr_value + new_value) / 2;
+println!("\t{final_value}");
+
+runners.insert(jill.clone(), final_value);
+
+let updater = runners.entry(jill.clone()).or_insert(0);
+*updater += new_value;
+*updater /= 2;
+
+println!("Jill's average after: {:?}", runners.get(&jill).unwrap());
+
+*/