Src. Change to exponential distribution

* Use crate *statrs*
* Provide *exp* function for exponential distribution
* Refactor function *normalize*
* Call by reference in *output* function

diff --git a/src/main.rs b/src/main.rs
index 949ac538cc69e3d66c66968aaa1e31791384f24a..a3d96977447a35970e4c6e796455b05d28660fde 100644 (file)
--- a/src/main.rs
+++ b/src/main.rs
@@ -4,6 +4,8 @@
 
 use std::io; // bring flush() into scope with `use std::io::Write`
 use std::io::prelude::*; // Bring `std::io::BufRead` in scope
+use statrs::distribution::{Exp, ContinuousCDF}; // Continuous needed for pdf
+// use statrs::statistics::Distribution;
 
 fn input() -> Vec<String> {
     // Consider datastructure some list of strings
@@ -12,34 +14,59 @@ fn input() -> Vec<String> {
     v
 }
 
-fn output(prio: Vec<f64>, ranked: Vec<String>) {
+fn output(prio: &Vec<f64>, ranked: &Vec<String>) {
     for (p, l) in prio.iter().zip(ranked.iter()) {
        println!("{:2.0} %\t{}", p * 100.0, l);
     }
 }
 
+fn normalize(mut arg: Vec<f64>) -> Vec<f64> {
+    let mut sum = 0.0;
+    for v in &arg {
+       sum += v;
+    }
+    for i in 0..arg.len() {
+       arg[i] /= sum;
+    }
+    arg
+}
+
+
 fn delta(n: i32) -> Vec<f64> {
-    let mut ret: Vec<f64> = Vec::new();
-    for _i in 0..n {
-       ret.push(1.0 / n as f64);
+    let mut prio: Vec<f64> = Vec::new();
+    const MEAN: f64 = 1.0; // unessential thanks to normalization
+    for i in 1..n + 1 {
+       prio.push(MEAN);
     }
-    ret
+    prio.reverse();
+    normalize(prio)
 }
 
+fn exp(n: i32) -> Vec<f64> {
+    const RATE: f64 = 1.0; // rate is unessential thanks to normalization
+    let mut prio: Vec<f64> = Vec::new();
+    let dist = Exp::new(RATE).unwrap();
+    for i in 1..n + 1 {
+       let f = i as f64 / (n as f64 + 1.0);
+       let x = dist.inverse_cdf(f);
+       prio.push(x);
+    }
+    prio.reverse();
+    normalize(prio)
+}
+
+
 fn main() {
+
     let ranked: Vec<String> = input();
     let num = ranked.len() as i32;
-    let prio = delta(num);
-    for p in prio.iter() {
-       eprint!("{} ", p);
-    }
-    eprintln!("");
-    for l in ranked.iter() {
-       eprint!("{} ", l);
+    let _prio1 = delta(num);
+    let prio2 = exp(num);
+
     }
     eprintln!("");
     eprintln!("That was {} items: {}", num, prio[0]);
 
-    output(prio, ranked);
+    output(&prio2, &ranked);
 
 }