Need help searching for values in file then adding to line

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http://www.unix.com – Hello! I'm currently trying to organize data for some bio research, but I'm not sure how to compare a value to values in a file. So what I have are 2 arrays, one array contains NM numbers and can be referenced as NM[#]. The other array has symbols, SYM[#]. I have a file for which it contains an NM number every other line and between each NM number, irrelevant information (but I need it in there still). What I need to do is match every NM[#] in my array to the NM number in the file, but also add :Sym[#] to the end of that line. The problem is, before each NM number in the file, there is a & (HowTos)