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1 package edu.unc.genomics.ngs;
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2
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3 import java.io.BufferedWriter;
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4 import java.io.IOException;
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5 import java.nio.charset.Charset;
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6 import java.nio.file.Files;
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7 import java.nio.file.Path;
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8 import java.util.Iterator;
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9
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10 import org.apache.log4j.Logger;
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11 import org.broad.igv.bbfile.WigItem;
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12
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13 import com.beust.jcommander.Parameter;
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14
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15 import edu.emory.mathcs.jtransforms.fft.FloatFFT_1D;
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16 import edu.unc.genomics.CommandLineTool;
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17 import edu.unc.genomics.Interval;
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18 import edu.unc.genomics.io.IntervalFile;
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19 import edu.unc.genomics.io.WigFile;
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20 import edu.unc.genomics.io.WigFileException;
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21
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22 public class PowerSpectrum extends CommandLineTool {
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23
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24 private static final Logger log = Logger.getLogger(PowerSpectrum.class);
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25
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26 @Parameter(names = {"-i", "--input"}, description = "Input file (Wig)", required = true)
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27 public WigFile inputFile;
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28 @Parameter(names = {"-l", "--loci"}, description = "Genomic loci (Bed format)", required = true)
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29 public IntervalFile<? extends Interval> loci;
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30 @Parameter(names = {"-o", "--output"}, description = "Output file (tabular)", required = true)
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31 public Path outputFile;
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32
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33 /**
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34 * Computes the power spectrum from FFT data
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35 * taking into accound even/odd length arrays
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36 * refer to JTransforms documentation for layout of the FFT data
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37 * @param f
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38 * @return
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39 */
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40 private float[] abs2(float[] f) {
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41 int n = f.length;
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42 float[] ps = new float[n/2+1];
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43 // DC component
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44 ps[0] = (f[0]*f[0]) / (n*n);
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45
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46 // Even
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47 if (n % 2 == 0) {
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48 for (int k = 1; k < n/2; k++) {
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49 ps[k] = f[2*k]*f[2*k] + f[2*k+1]*f[2*k+1];
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50 }
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51 ps[n/2] = f[1]*f[1];
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52 // Odd
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53 } else {
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54 for (int k = 1; k < (n-1)/2; k++) {
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55 ps[k] = f[2*k]*f[2*k] + f[2*k+1]*f[2*k+1];
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56 }
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57
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58 ps[(n-1)/2] = f[n-1]*f[n-1] + f[1]*f[1];
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59 }
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60
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61 return ps;
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62 }
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63
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64 public void run() throws IOException {
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65 try (BufferedWriter writer = Files.newBufferedWriter(outputFile, Charset.defaultCharset())) {
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66 log.debug("Computing power spectrum for each window");
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67 int skipped = 0;
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68 for (Interval interval : loci) {
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69 Iterator<WigItem> wigIter;
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70 try {
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71 wigIter = inputFile.query(interval);
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72 } catch (IOException | WigFileException e) {
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73 log.debug("Skipping interval: " + interval.toString());
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74 skipped++;
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75 continue;
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76 }
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77
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78 float[] data = WigFile.flattenData(wigIter, interval.getStart(), interval.getStop());
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79 // Compute the power spectrum
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80 FloatFFT_1D fft = new FloatFFT_1D(data.length);
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81 fft.realForward(data);
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82 float[] ps = abs2(data);
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83 // and normalize the power spectrum
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84 float sum = 0;
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85 for (int i = 1; i < ps.length; i++) {
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86 sum += ps[i];
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87 }
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88 for (int i = 1; i < ps.length; i++) {
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89 ps[i] /= sum;
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90 }
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91
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92 writer.write(interval.toBed());
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93 for (int i = 1; i < Math.min(ps.length, 40); i++) {
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94 writer.write("\t"+ps[i]);
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95 }
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96 writer.newLine();
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97 }
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98
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99 log.info("Skipped " + skipped + " intervals");
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100 }
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101 }
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102
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103 public static void main(String[] args) {
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104 new PowerSpectrum().instanceMain(args);
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105 }
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106 } |
