1use crate::stats::float::Float;
2use cast::{self, usize};
3
4/// A "view" into the percentiles of a sample
5pub struct Percentiles<A>(Box<[A]>)
6where
7 A: Float;
8
9// TODO(rust-lang/rfcs#735) move this `impl` into a private percentiles module
10impl<A> Percentiles<A>
11where
12 A: Float,
13 usize: cast::From<A, Output = Result<usize, cast::Error>>,
14{
15 /// Returns the percentile at `p`%
16 ///
17 /// Safety:
18 ///
19 /// - Make sure that `p` is in the range `[0, 100]`
20 unsafe fn at_unchecked(&self, p: A) -> A {
21 let _100 = A::cast(100);
22 debug_assert!(p >= A::cast(0) && p <= _100);
23 debug_assert!(self.0.len() > 0);
24 let len = self.0.len() - 1;
25
26 if p == _100 {
27 self.0[len]
28 } else {
29 let rank = (p / _100) * A::cast(len);
30 let integer = rank.floor();
31 let fraction = rank - integer;
32 let n = usize(integer).unwrap();
33 let &floor = self.0.get_unchecked(n);
34 let &ceiling = self.0.get_unchecked(n + 1);
35
36 floor + (ceiling - floor) * fraction
37 }
38 }
39
40 /// Returns the percentile at `p`%
41 ///
42 /// # Panics
43 ///
44 /// Panics if `p` is outside the closed `[0, 100]` range
45 pub fn at(&self, p: A) -> A {
46 let _0 = A::cast(0);
47 let _100 = A::cast(100);
48
49 assert!(p >= _0 && p <= _100);
50 assert!(self.0.len() > 0);
51
52 unsafe { self.at_unchecked(p) }
53 }
54
55 /// Returns the interquartile range
56 pub fn iqr(&self) -> A {
57 let q1 = self.at(A::cast(25));
58 let q3 = self.at(A::cast(75));
59
60 q3 - q1
61 }
62
63 /// Returns the 50th percentile
64 pub fn median(&self) -> A {
65 self.at(A::cast(50))
66 }
67
68 /// Returns the 25th, 50th and 75th percentiles
69 pub fn quartiles(&self) -> (A, A, A) {
70 (
71 self.at(A::cast(25)),
72 self.at(A::cast(50)),
73 self.at(A::cast(75)),
74 )
75 }
76}
77