def expand_header(row):
    """Parse the header information.

    Args:
        List[str]: sambamba BED header row

    Returns:
        dict: name/index combos for fields
    """
    # figure out where the sambamba output begins
    sambamba_start = row.index('readCount')
    sambamba_end = row.index('sampleName')
    coverage_columns = row[sambamba_start + 2:sambamba_end]
    thresholds = {int(column.replace('percentage', '')): row.index(column)
                  for column in coverage_columns}
    keys = {
        'readCount': sambamba_start,
        'meanCoverage': sambamba_start + 1,
        'thresholds': thresholds,
        'sampleName': sambamba_end,
        'extraFields': slice(3, sambamba_start)
    }
    return keys