I have data sets of 5000+ lines and varying lengths In terms of elements existing in any given line of data. I have stored each line of data as a `list` where each element is stored as an `index` (i.e. some lines may have 5 indices where others may have 20). Index 2 is **always** the elapsed time for that line of data.

My script currently `iterates` through the data set using a `for` loop as a means to structure the data. See below:

```
f = open(fn)
for line in iter(f):

    remove_blanks = ['']
    entries = line.split()
    ''.join([i for i in entries if i not in remove_blanks])
    trash = (entries[0], entries[1])
    time = int(entries[2])  # Time expressed as elapsed time in milliseconds
    column = [int(v) for v in entries[3:]]

```

Where the lines (from the data set) the script iterates through look something like

`x y #time a b`

`d e #time f g h`

Which are then put into lists like

`['x', 'y', '#time', 'a', 'b']`

`['d', 'e', '#time', 'f', 'g', 'h']`

I would like to iteratively subtract the initial time (non-zero) from the time present in any given line. For example, I would like to do 
`(#time on line x) - (#time on line 0)` and `print` the elapsed time for each line. Perhaps this can be done before the data structure is created, I am not sure. 

Please help!

Thanks