/**
* Computes an allele biased version of the given pileup
*
* @param pileup the original pileup
* @param downsamplingFraction the fraction of total reads to remove per allele
* @return allele biased pileup
*/
public static ReadBackedPileup createAlleleBiasedBasePileup(
final ReadBackedPileup pileup, final double downsamplingFraction) {
// special case removal of all or no reads
if (downsamplingFraction <= 0.0) return pileup;
if (downsamplingFraction >= 1.0)
return new ReadBackedPileupImpl(pileup.getLocation(), new ArrayList<PileupElement>());
final PileupElementList[] alleleStratifiedElements = new PileupElementList[4];
for (int i = 0; i < 4; i++) alleleStratifiedElements[i] = new PileupElementList();
// start by stratifying the reads by the alleles they represent at this position
for (final PileupElement pe : pileup) {
final int baseIndex = BaseUtils.simpleBaseToBaseIndex(pe.getBase());
if (baseIndex != -1) alleleStratifiedElements[baseIndex].add(pe);
}
// make a listing of allele counts and calculate the total count
final int[] alleleCounts = calculateAlleleCounts(alleleStratifiedElements);
final int totalAlleleCount = (int) MathUtils.sum(alleleCounts);
// do smart down-sampling
final int numReadsToRemove = (int) (totalAlleleCount * downsamplingFraction); // floor
final int[] targetAlleleCounts = runSmartDownsampling(alleleCounts, numReadsToRemove);
final HashSet<PileupElement> readsToRemove = new HashSet<PileupElement>(numReadsToRemove);
for (int i = 0; i < 4; i++) {
final PileupElementList alleleList = alleleStratifiedElements[i];
// if we don't need to remove any reads, then don't
if (alleleCounts[i] > targetAlleleCounts[i])
readsToRemove.addAll(
downsampleElements(
alleleList, alleleCounts[i], alleleCounts[i] - targetAlleleCounts[i]));
}
// we need to keep the reads sorted because the FragmentUtils code will expect them in
// coordinate order and will fail otherwise
final List<PileupElement> readsToKeep =
new ArrayList<PileupElement>(totalAlleleCount - numReadsToRemove);
for (final PileupElement pe : pileup) {
if (!readsToRemove.contains(pe)) {
readsToKeep.add(pe);
}
}
return new ReadBackedPileupImpl(
pileup.getLocation(), new ArrayList<PileupElement>(readsToKeep));
}
