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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def parallel_variantcall_region(samples, run_parallel):
 """Perform variant calling and post-analysis on samples by region. """

    to_process, extras = _dup_samples_by_variantcaller(samples)
    split_fn = _split_by_ready_regions(".vcf.gz", "work_bam", get_variantcaller)
    samples = _collapse_by_bam_variantcaller(
        grouped_parallel_split_combine(to_process, split_fn,
                                       multi.group_batches, run_parallel,
                                       "variantcall_sample", "concat_variant_files",
                                       "vrn_file", ["region", "sam_ref", "config"]))
    return extras + samples