Third update on iterators - HASHMAP

examples/hashmap/iterator.c

@@ -0,0 +1,230 @@
+/**
+ * iterator.c
+ *
+ * Creation Date: 14/05/2019
+ *
+ * Authors:
+ * Leonardo Vencovsky (https://github.com/LeoVen)
+ *
+ * Iterator Example
+ */
+#include "hashmap.h"
+#include <stdio.h>
+#include <inttypes.h>
+
+// Int hash function
+size_t inthash(int t)
+{
+    size_t a = t;
+    a += ~(a << 15);
+    a ^= (a >> 10);
+    a += (a << 3);
+    a ^= (a >> 6);
+    a += ~(a << 11);
+    a ^= (a >> 16);
+    return a;
+}
+
+// Int compare function
+int intcmp(int a, int b)
+{
+    return a - b;
+}
+
+// Creates a hashmap of integers
+HASHMAP_GENERATE(hm, hashmap, /* FMOD */, int, double)
+
+int main(int argc, char const *argv[])
+{
+    // Create a new hashmap with an initial capacity of 100
+    hashmap *my_map = hm_new(100, 0.6, intcmp, inthash);
+
+    // Add pairs to the hashmap
+    for (int i = 0; i < 20; i++)
+    {
+        // Map integers to doubles
+        hm_insert(my_map, i, (double)i / 10.0);
+    }
+
+    // Iterate from the start (index 0) to the end (index count - 1) of the hashmap
+    for (hashmap_iter it = my_map->it_start(my_map); // Initialize iterator 'it' to the start of the hashmap
+         !hm_iter_end(&it);                          // Conditional stop (until it is not at the end)
+         hm_iter_next(&it))                          // Iterator goes one position forward
+    {
+        // Access the current key
+        int k = hm_iter_key(&it);
+
+        // Access the current value
+        double v = hm_iter_value(&it);
+
+        // Access the current index (index is relative to all the pairs in the iteration)
+        size_t i = hm_iter_index(&it);
+
+        // Print hashmap
+
+        // Index is useful in situations like this
+        // If it is the first pair
+        if (i == 0)
+            printf("[ {%d:%.2lf}, ", k, v);
+        // If it is the last pair
+        else if (i == hm_count(my_map) - 1)
+            printf("{%d:%.2lf} ]\n", k, v);
+        // For pairs at the middle
+        else
+            printf("{%d:%.2lf}, ", k, v);
+    }
+
+    // Index can also be used to iterate over a certain portion of a collection
+    size_t limit = hm_count(my_map) / 2;
+    for (hashmap_iter it = my_map->it_start(my_map); !hm_iter_end(&it); hm_iter_next(&it))
+    {
+        // Access the current key
+        int k = hm_iter_key(&it);
+
+        // Access the current value
+        double v = hm_iter_value(&it);
+
+        // Access the current index (index is relative to all the pairs in the iteration)
+        size_t i = hm_iter_index(&it);
+
+        // Print hashmap up until limit
+
+        // If it is the first pair
+        if (i == 0)
+            printf("[ {%d:%.2lf}, ", k, v);
+        // If it is the last pair
+        else if (i == limit - 1) // -1 because index is 0 based and we want half of the hashmap
+        {
+            printf("{%d:%.2lf} ]\n", k, v);
+            break;
+        }
+        // For pairs at the middle
+        else
+            printf("{%d:%.2lf}, ", k, v);
+    }
+
+    // Going backwards
+    for (hashmap_iter it = my_map->it_end(my_map); // Initialize iterator 'it' to the end of the hashmap
+         !hm_iter_start(&it);                      // Conditional stop (until it is not at the start)
+         hm_iter_prev(&it))                        // Iterator goes one position backwards
+    {
+        // Access the current key
+        int k = hm_iter_key(&it);
+
+        // Access the current value
+        double v = hm_iter_value(&it);
+
+        // Access the current index (index is relative to all the pairs in the iteration)
+        size_t i = hm_iter_index(&it);
+
+        // Print hashmap
+        // Note how the conditions for the first and last pairs are simply swapped
+        // Because iterating backwards make the first pair be the index count - 1
+        // and the last one be the index 0
+
+        // If it is the first pair
+        if (i == hm_count(my_map) - 1)
+            printf("[ {%d:%.2lf}, ", k, v);
+        // If it is the last pair
+        else if (i == 0)
+            printf("{%d:%.2lf} ]\n", k, v);
+        // For pairs at the middle
+        else
+            printf("{%d:%.2lf}, ", k, v);
+    }
+
+    // You can also use iterators in a while loop
+    // But to do so you must declare the iterator struct outside the loop first
+    hashmap_iter it;
+
+    // You have three options:
+    // - Initialize it using the functions provided by the hashmap [ my_map->it_start() and my_map->it_end() ]
+    // - Initialize it using the init() function (when the iterator is already allocated)
+    // - Initialize it using the new() function (allocates on the heap, pointers only)
+
+    it = my_map->it_start(my_map);
+    it = my_map->it_end(my_map);
+
+    // This is equivalent to it_start()
+    hm_iter_init(&it, my_map);
+
+    // For pointers
+    // Also equivalent to it_start()
+    hashmap_iter *iter = hm_iter_new(my_map);
+
+    // The actual while loop
+    while (!hm_iter_end(iter))
+    {
+        // Accessing pairs
+        int k = hm_iter_key(iter);
+        double v = hm_iter_value(iter);
+        size_t i = hm_iter_index(iter);
+
+        // Print index and key value pair
+        printf("hashmap[%2" PRIuMAX "] = { %2d : %.2lf }\n", i, k, v);
+
+        // Move iterator forwards
+        hm_iter_next(iter);
+    }
+
+    // Send the iterator to the start of the hashmap
+    hm_iter_to_start(iter);
+
+    // Send the iterator to the end of the hashmap
+    hm_iter_to_end(iter);
+
+    // Backwards loop
+    while (!hm_iter_start(iter))
+    {
+        // Accessing pairs
+        int k = hm_iter_key(iter);
+        double v = hm_iter_value(iter);
+        size_t i = hm_iter_index(iter);
+
+        // Print index and the key value pair
+        printf("hashmap[%2" PRIuMAX "] = { %2d : %.2lf }\n", i, k, v);
+
+        // Move iterator backwards
+        hm_iter_prev(iter);
+    }
+
+    // Certain iterators also allow you to modify the contents it is iterating over
+    // Exceptions are collections that depend of the current state of the pair
+    // like tree-based collections and heap (collections that have some kind of ordering).
+    // You also can't change the keys of an associative collection
+
+    // Change every value where its key is divisible by 3 to the number 7
+    for (hm_iter_to_start(&it); !hm_iter_end(&it); hm_iter_next(&it))
+    {
+        // Get current key
+        int k = hm_iter_key(&it);
+
+        // Get a reference to the current value
+        double *v = hm_iter_rvalue(&it);
+
+        if (k % 3 == 0)
+            *v = 7;
+    }
+
+    // Now print it to see the difference
+    for (hashmap_iter it = my_map->it_start(my_map); !hm_iter_end(&it); hm_iter_next(&it))
+    {
+        int k = hm_iter_key(&it);
+        double v = hm_iter_value(&it);
+        size_t i = hm_iter_index(&it);
+
+        if (i == 0)
+            printf("[ {%d:%.2lf}, ", k, v);
+        else if (i == hm_count(my_map) - 1)
+            printf("{%d:%.2lf} ]\n", k, v);
+        else
+            printf("{%d:%.2lf}, ", k, v);
+    }
+
+    // Dispose the iterator called by hm_iter_new()
+    hm_iter_free(iter);
+    // Dispose the hashmap created
+    hm_free(my_map);
+
+    return 0;
+}