Hash join: Difference between revisions

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 =={{header|Rust}}==
 <lang rust>use std::collections::HashMap;
+use std::hash::Hash;
+// If you know one of the tables is smaller, it is best to make it the second parameter.
+fn hash_join<A, B, K>(first: &[(K, A)], second: &[(K, B)]) -> Vec<(A, K, B)>
+where
+    K: Hash + Eq + Copy,
+    A: Copy,
+    B: Copy,
+{
+    let mut hash_map = HashMap::new();
-fn main() {
-    let table_a = vec![
-        (27, "Jonah"), (18, "Alan"), (28, "Glory"),
-        (18, "Popeye"), (28, "Alan")
-    ];
-    let table_b = vec![
-        ("Jonah", "Whales"), ("Jonah", "Spiders"), ("Alan", "Ghosts"),
-        ("Alan", "Zombies"), ("Glory", "Buffy")
-    ];
     // hash phase
+    for &(key, val_a) in second {
-    let mut h = HashMap::new();
+        // collect all values by their keys, appending new ones to each existing entry
-    for (i, a) in table_a.iter().enumerate() {
-        h.entry(a.1).or_insert_with(Vec::new).push(i);
+        hash_map.entry(key).or_insert_with(Vec::new).push(val_a);
     }
+    let mut result = Vec::new();
     // join phase
-    for b in table_b {
+    for &(key, val_b) in first {
-        if let Some(vals) = h.get(b.0) {
+        if let Some(vals) = hash_map.get(&key) {
-            for &val in vals {
+            let tuples = vals.iter().map(|&val_a| (val_b, key, val_a));
-                let a = table_a.get(val).unwrap();
+            result.extend(tuples);
-                println!("{:?} {:?}", a, b);
-            }
         }
     }
+    result
 }
-</lang>
+fn main() {
+    let table1 = [("Jonah", 27), ("Alan", 18), ("Glory", 28), ("Popeye", 18), ("Alan", 28)];
+    let table2 = [
+        ("Jonah", "Whales"), ("Jonah", "Spiders"), ("Alan", "Ghosts"),
+        ("Alan", "Zombies"), ("Glory", "Buffy")
+    ];
+    let result = hash_join(&table1, &table2);
+    println!("Age | Character Name | Nemesis");
+    println!("----|----------------|--------");
+    for (age, name, nemesis) in result {
+        println!("{:<3} | {:^14} | {}", age, name, nemesis);
+    }
+}</lang>
 {{out}}
+<pre>Age | Character Name | Nemesis
-<pre>
+----|----------------|--------
-(27, "Jonah") ("Jonah", "Whales")
-(27, "Jonah") ("Jonah", "Spiders")
+|     Jonah      | Whales
+|     Jonah      | Spiders
-(18, "Alan") ("Alan", "Ghosts")
-(28, "Alan") ("Alan", "Ghosts")
+|      Alan      | Ghosts
-(18, "Alan") ("Alan", "Zombies")
+|      Alan      | Zombies
+|     Glory      | Buffy
-(28, "Alan") ("Alan", "Zombies")
+|      Alan      | Ghosts
-(28, "Glory") ("Glory", "Buffy")
+|      Alan      | Zombies</pre>
-</pre>
 =={{header|Scala}}==