interpn 0.11.0

N-dimensional interpolation/extrapolation methods, no-std and no-alloc compatible.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180

//! Piecewise-constant 1D interpolators

use num_traits::Float;

use super::{Extrap, Grid1D, GridSample, Interp1D};

/// Hold-last piecewise constant interpolation
pub struct Left1D<G> {
    grid: G,
}

impl<G> Left1D<G> {
    pub fn new(grid: G) -> Self {
        Self { grid }
    }
}

impl<'a, T, G> Interp1D<'a, T, G> for Left1D<G>
where
    T: Float,
    G: Grid1D<'a, T>,
{
    #[inline]
    fn eval_one(&self, loc: T) -> Result<T, &'static str> {
        let GridSample {
            x0: _,
            y0,
            x1: _,
            y1,
            extrap,
        } = self.grid.at(loc)?;

        let v = match extrap {
            Extrap::OutsideHigh => y1,
            _ => y0,
        };

        Ok(v)
    }
}

/// Hold-next piecewise-constant interpolation
pub struct Right1D<G> {
    grid: G,
}

impl<G> Right1D<G> {
    pub fn new(grid: G) -> Self {
        Self { grid }
    }
}

impl<'a, T, G> Interp1D<'a, T, G> for Right1D<G>
where
    T: Float,
    G: Grid1D<'a, T>,
{
    #[inline]
    fn eval_one(&self, loc: T) -> Result<T, &'static str> {
        let GridSample {
            x0: _,
            y0,
            x1: _,
            y1,
            extrap,
        } = self.grid.at(loc)?;

        let v = match extrap {
            Extrap::OutsideLow => y0,
            _ => y1,
        };

        Ok(v)
    }
}

/// Nearest-value piecewise-constant interpolation.
/// In the event of a tie, the left value is taken.
pub struct Nearest1D<G> {
    grid: G,
}

impl<G> Nearest1D<G> {
    pub fn new(grid: G) -> Self {
        Self { grid }
    }
}

impl<'a, T, G> Interp1D<'a, T, G> for Nearest1D<G>
where
    T: Float,
    G: Grid1D<'a, T>,
{
    #[inline]
    fn eval_one(&self, loc: T) -> Result<T, &'static str> {
        let GridSample { x0, y0, x1, y1, .. } = self.grid.at(loc)?;

        let dx0 = (loc - x0).abs();
        let dx1 = (loc - x1).abs();

        let v = match dx1 >= dx0 {
            true => y0,
            false => y1,
        };

        Ok(v)
    }
}

#[cfg(test)]
mod test {
    use crate::one_dim::{Interp1D, RegularGrid1D};
    use crate::testing::{randn, rng_fixed_seed};
    use crate::utils::linspace;

    use super::{Left1D, Nearest1D, Right1D};

    #[test]
    fn test_hold_1d() {
        let rng = &mut rng_fixed_seed();

        let n = 77;

        let vals = &randn::<f64>(rng, n)[..];

        // Regular grid
        let (start, stop) = (-3.14, 314.0);
        let x_reg = linspace(start, stop, n);
        let g_reg = RegularGrid1D::new(x_reg[0], x_reg[1] - x_reg[0], vals).unwrap();

        // Interpolators
        let left_reg = Left1D::new(g_reg);
        let right_reg = Right1D::new(g_reg);
        let nearest_reg = Nearest1D::new(g_reg);

        // Observations under both interpolation and extrapolation
        let mut locs = randn::<f64>(rng, 3 * n);
        locs.iter_mut()
            .for_each(|x| *x = (*x * 2.0 * (stop - start)) + 2.0 * start);

        let y_lreg = left_reg.eval_alloc(&locs).unwrap();
        let y_rreg = right_reg.eval_alloc(&locs).unwrap();
        let y_nreg = nearest_reg.eval_alloc(&locs).unwrap();

        // Check
        for i in 0..locs.len() {
            let loc = locs[i];
            let j: usize = ((x_reg.partition_point(|v| v < &loc) as isize - 1).max(0) as usize)
                .min(x_reg.len() - 2);

            let xleft = x_reg[j];
            let xright = x_reg[j + 1];
            let yleft = vals[j];
            let yright = vals[j + 1];

            // Interpolation
            if loc >= x_reg[0] && loc <= x_reg[n - 1] {
                assert!(
                    loc >= xleft && loc <= xright,
                    "Didn't find the correct cell"
                );

                assert_eq!(y_lreg[i], yleft);
                assert_eq!(y_rreg[i], yright);
            } else if loc > x_reg[n - 1] {
                assert_eq!(y_lreg[i], yright);
                assert_eq!(y_rreg[i], yright);
            } else if loc < x_reg[0] {
                assert_eq!(y_lreg[i], yleft);
                assert_eq!(y_rreg[i], yleft);
            }

            let y_nearest = match (loc - xleft) <= (xright - loc) {
                true => yleft,
                false => yright,
            };
            assert_eq!(y_nreg[i], y_nearest);
        }
    }
}