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

That (like most of the answers) assumes that the lines in the second file are numbered consecutively with no numbers missing. I wasn't sure from the question whether that was the case, or if when he said, "The file which I am appending a single column has the line number in the first column," he meant it had the number of the line it needed to be attached to.

In other words, the second file could be:

2 red
4 brown
3 blue
6 orange
7 yellow

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If 'yellow' is supposed to be appended to the 7th line of file1, then sorting file2 numerically and stepping through both files equally won't work, because 'lines' 1 and 5 are missing.

By using the numbers in file2 as keys in a lookup hash, it doesn't matter if file2 is missing a number somewhere. I guess it really just depends on how sure you are that you can count on the numbers truly being line numbers.

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Re^4: Merging larges files by columns
by Marshall (Canon) on Sep 19, 2011 at 00:59 UTC
    That (like most of the answers) assumes that the lines in the second file are numbered consecutively with no numbers missing.
    Not so. I suggested sorting file 2 so that the numbers are always increasing. That way a simple walker program suffices and could account for missing numbers. The simple sort strategy is often very effective as the system sort command is usually efficient enough - certainly will be a huge improvement upon read file2 N times!!

    In this case, the original poster seems to have disappeared and we are left speculating about requirements that we can't know unless the OP tells us.

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