smart_arrays_peaks 2.0.5

Provides functions to detect (search, pick) peaks (maximum values) in one- or two-dimensional arrays, also suitable for noisy data.

example/example.dart

// Copyright (c) 2019, Dr. Bruno Guigas. All rights reserved. Use of this source
// code is governed by a BSD-style license that can be found in the LICENSE file.
import 'package:smart_arrays_peaks/smart_arrays_peaks.dart';
import 'dart:typed_data';
import 'dart:math' as math;

/// Demonstrates peak picking for 1D and 2D arrays.
main() {
  // generate noisy sine wave ([noise] is a fraction of [ampl])
  Float64List genSine(
      double ampl, double phase, int nperiods, int nxvalues, double noise) {
    math.Random rand = math.Random();
    double xmax = 2 * math.pi * nperiods, x, y;
    Float64List sine = new Float64List(nxvalues);
    for (int i = 0; i < nxvalues; i++) {
      x = (i * xmax) / nxvalues;
      y = ampl * math.sin(x + phase);
      // add noise between -1 and 1
      sine[i] = y + noise * ampl * (2 * rand.nextDouble() - 1.0).sign;
    }
    return sine;
  }

  // Example 1D peak picking
  Float64List array = genSine(100.0, 0.0, 10, 1000, 0.005); // sine with noise

  // pick peaks: use noise discriminator 2.0 to suppress "noise peaks".
  List<int> peakIndices = PeakPicker1D.detectPeaks(
      array, 0, array.length, 2.0, 0.001, PeakPicker1D.PICK_POSNEG, 0);

  // print result: we expect 10 minima with values around -100 and 10 maxima
  // around +100.
  for (int i = 0; i < peakIndices.length; i++) {
    int ipeak = peakIndices[i];
    print("Peak # / index / value: " +
        "${i + 1} / $ipeak / ${array[ipeak].toStringAsFixed(2)}");
  }
  print("");

  // Example 2D peak picking
  final List<List<double>> PEAK_2D = [
    [70, 80, 75, 73],
    [80, 85, 90, 91],
    [83, 100, 90, 80],
    [81, 95, 93, 92]
  ]; // a sample 2D peak

  // Create a matrix with 2 peaks at row/col positions 10/20 and 20/15
  final int NROWS = 32, NCOLS = 41;
  List<Float64List> matrix = List(NROWS);
  for (int i = 0; i < NROWS; i++) {
    matrix[i] = Float64List(NCOLS);
    if (i == 8 || i == 9 || i == 10 || i == 11)
      matrix[i].setRange(19, 19 + PEAK_2D[0].length - 1, PEAK_2D[i - 8]);
    if (i == 18 || i == 19 || i == 20 || i == 21)
      matrix[i].setRange(14, 14 + PEAK_2D[0].length - 1, PEAK_2D[i - 18]);
  }

  // pick peaks
  List<List<int>> peakIndices2D = PeakPicker2D().detectPeaks(
      matrix, 0, NROWS, 0, NCOLS, 0.0, 0.0, PeakPicker1D.PICK_POSNEG, 0);

  // print result: we expect 2 maxima with value 100 at positions 10/20 and 20/15
  for (int i = 0; i < peakIndices2D.length; i++) {
    int row = peakIndices2D[i][0];
    int col = peakIndices2D[i][1];
    print("2D Peak # / row /col / value: " +
        "${i + 1} / $row / $col / ${matrix[row][col].toStringAsFixed(2)}");
  }
}