First, if you are creating the file, you should think about doing this while you're getting your data, before writing to the file.
If you want to handle the file, you should start by reading it as a text spreadsheet. You can modify the Read from spreadsheet VI to read text files by double clicking it and following the instructions on its diagram.
I assume the lines are sorted by date and time. If they're not, this can also be taken care of.
You should now have a 2D string array 4 columns wide. Wire it into a for loop and create a shift register with an empty 2D string array wired into it. This will be your new array. The first column will be the reference array. Use Index Array to get the number of each element and search the reference array (use index array with 0 wired into the column input to get it) for that number. If you get -1, Insert the entire row into the new array. If you get another number, Replace that row in the new array with the current row.
Sorting by the first column can be done basically in the same way - create a 2D array the size of your new array and wire it into a shift register in a new for loop. Do a Sort 1D Array on the first column of the new array and wire it into the for loop. Use search 1D array to find where each sorted element was in the original array and use Replace Array Subset to replace it.
Now, save the 2D array back into the file.
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