A function representing the pipeline of four steps including GC bias correction, sample filtration, PCA and contig filtration
pipeline(Y, i)a named list
samples: final list of filtered samples
correct_ys: dataframe with correct Y values per contig/sample
pc1: PC1 results of PCA per contig
pc1_range: range of PC1
samples_y: samples filtered for reliable coverage
a matrix of coverages
cutoff of filtering samples changes according to parameter i; i=1, cutoffRatio is 0.5; i=2, cutoffRatio is 1 as contig is clean