iterate bam file over set of regions

[Peter]

Creating a bam read iterator is relatively expensive because it has to seek the location of the first read (utilizing the index but still). When doing that repeatedly, say to iterate over all exons, it might be cheaper to just read through to the next region rather than create a new BamReadIterator which seeks the location etc. This depends on how many reads there are between current and next region. The idea here is to have an iterator that reads through the bam file when that is fastest and seeks via the bam index when that is fastest.

[Peter]

From htslib v1.7 there is a multi-region iterator:

The new structure takes a list of regions and
iterates over all, deduplicating reads in the process, and producing a
full list of file offset intervals. This is usually much faster than
repeatedly using the old single-region iterator on a series of regions.