def fq_merge(R1, R2):
    """
    merge separate fastq files
    """
    c = itertools.cycle([1, 2, 3, 4])
    for r1, r2 in zip(R1, R2):
        n = next(c)
        if n == 1:
            pair = [[], []]
        pair[0].append(r1.strip())
        pair[1].append(r2.strip())
        if n == 4:
            yield pair