I would suggest sorting file2 by number. unix sort command. There is a Windows version also.

The idea is to have both file1 and file2 in an order such that it is just a stepwise ladder walk. Our mythical ladder walker has one foot on ladder1 and one foot on ladder2 and if a foot moves, it moves upward.

This takes a long time: 

foreach line in file1...
{
  loop through lines in file2...
  {
     ...many comparisons... decide which one is next
  }
}

[download]
A step-wise walker algorithm is a merge of 2 sorted files and is much faster because all that is needed is to decide who goes next, like 2 cars at a stop sign. 
foreach line in file1...
{
    # insert file2 line(s) that should go before the
    # current line from file1
    while {the current line in file2 is "next" in total order}
    {   
        output that line from file2; 
        move to next line in file2
    }
    output the file1 line
}
output rest of file2 lines (if any)

[download]

In reply to Re^2: Merging larges files by columns by Marshall
in thread Merging larges files by columns by ScottJohn

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