calc frequency of letters

src/wlist/mod.rs

@@ -44,7 +44,22 @@ pub trait WordList: Clone + std::fmt::Debug + Default {
         for (k, v) in wpairs {
             hm.insert(k.into(), *v);
         }
-        WordMap::new(hm)
+        WordMap::from(hm)
     }
     fn get_word(&self, word: &Word) -> Option<WordData>;
+    fn letter_frequency(&self) -> WordMap {
+        // PERF: this function has complexity O(n²)!
+        let mut cmap: HashMap<char, usize> = HashMap::new();
+        // count the chars in each word
+        for word in self.wordmap().iter() {
+            for c in word.0.chars() {
+                if let Some(inner_value) = cmap.get_mut(&c) {
+                    *inner_value += 1;
+                }
+            }
+        }
+        // make all chars to strings
+        let cmap: HashMap<Word, usize> = cmap.into_iter().map(|p| (p.0.to_string(), p.1)).collect();
+        WordMap::from_absolute(cmap)
+    }
 }

src/wlist/word.rs

@@ -21,8 +21,10 @@ pub struct WordMap {
 }
 
 impl WordMap {
-    pub fn new(inner: HashMap<Word, Frequency>) -> Self {
-        Self { inner }
+    pub fn new() -> Self {
+        Self {
+            inner: HashMap::new(),
+        }
     }
     pub fn keys(&self) -> std::collections::hash_map::Keys<'_, String, Frequency> {
         self.inner.keys()
@@ -70,6 +72,12 @@ impl WordMap {
             None => None,
         }
     }
+    pub fn from_absolute(abs: HashMap<Word, usize>) -> Self {
+        let n: f64 = abs.keys().len() as f64;
+        let relative: HashMap<Word, Frequency> =
+            abs.into_iter().map(|p| (p.0, p.1 as f64 / n)).collect();
+        relative.into()
+    }
 }
 
 impl std::fmt::Debug for WordMap {
@@ -89,3 +97,9 @@ impl std::fmt::Debug for WordMap {
         )
     }
 }
+
+impl From<HashMap<Word, Frequency>> for WordMap {
+    fn from(value: HashMap<Word, Frequency>) -> Self {
+        Self { inner: value }
+    }
+}