cdf | add util to calculate the cumulative distribution function values

src/bin/cdf.rs

@@ -0,0 +1,61 @@
+use color_eyre::eyre::Result;
+use std::io;
+use std::io::BufRead;
+use std::io::BufReader;
+use std::io::BufWriter;
+use std::io::Write;
+
+/// reads input from stdin
+/// writes output to stdout
+fn main() -> Result<()> {
+    let stdin = io::stdin();
+    let rdr = BufReader::new(stdin);
+
+    // read the data
+    let mut data = Vec::new();
+    for line in rdr.lines() {
+        let line = line?;
+        let val = line.parse::<f64>()?;
+        data.push(val);
+    }
+    data.sort_unstable_by(|a, b| a.partial_cmp(b).unwrap());
+
+    // calculate frequency distribution
+    let markers: &[f64] = &[
+        0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70,
+        0.75, 0.80, 0.85, 0.90, 0.95, 1.00,
+    ];
+
+    // calculate the marker values
+    let min_val = data[0];
+    let max_val = data
+        .last()
+        .expect("atleast one value needs to be provided to calculate the stats");
+    let mut marker_vals: Vec<f64> = Vec::with_capacity(markers.len());
+
+    // identify the marker-vals corresponding to each marker
+    for m in markers {
+        let target = min_val + m * (max_val - min_val);
+        let m_idx = match data.binary_search_by(|probe| probe.partial_cmp(&target).unwrap()) {
+            Ok(idx) | Err(idx) => idx,
+        };
+        marker_vals.push(data[m_idx]);
+    }
+
+    // now we just count the values that are less that each marker-val
+    let mut cdf_cnts: Vec<f64> = Vec::with_capacity(markers.len());
+    for mv in marker_vals {
+        let cnt = data.iter().take_while(|val| **val <= mv).count();
+        #[allow(clippy::cast_precision_loss)]
+        let percent = cnt as f64 / data.len() as f64;
+        cdf_cnts.push(percent);
+    }
+
+    // output
+    let mut w = BufWriter::new(io::stdout());
+    for (marker, percent) in markers.iter().zip(cdf_cnts.iter()) {
+        writeln!(&mut w, "{marker},{percent}")?;
+    }
+
+    Ok(())
+}