I've written perl code that collects interface packet counts via SNMP.   So far, so good.   Now I'm asking for y'alls wisdom on getting the *real* data out of the following csv.

What I need to do goes something like this (in english):

Read the first and second lines
    deltaTime2 = epochSec2 - epochSec1
    Bps2 = (ifInOctets2 + ifOutOctets2)/deltaTime2
Read the second and third lines
    deltaTime3 = epochSec3 - epochSec2
    Bps3 = (ifInOctets3 + ifOutOctets3)/deltaTime3
Read the third and fourth lines
    deltaTime4 = epochSec4 - epochSec3
    Bps3 = (ifInOctets4 + ifOutOctets4)/deltaTime4
Lather, rinse, repeat...

In a past life, I'd have used Excel for the calculations {oh, the shame} but now I'd *really* like to do this in a Perlish manner.     Doing the simple arithmetic in Perl is easy.   I imagine the control code might involve split() and a LoL, but am quite unclear on where to start.   Any clueful monks care to point me in a good direction?
    cheers,
    Don
    striving toward Perl Adept
    (it's pronounced "why-bick")

Collected data csv: 

date,time,epochSec,device,ifIndex,ifInOctets,ifOutOctets,
2001-08-10,18:15:00,997485300,boston,141,1916238333,2743654663,
2001-08-10,18:18:12,997485492,boston,141,1917535505,2744657633,
2001-08-10,18:21:23,997485683,boston,141,1919320447,2747461877,
2001-08-10,18:24:34,997485874,boston,141,1921869420,2748722088,
2001-08-10,18:27:46,997486066,boston,141,1925884600,2764661750,
2001-08-10,18:30:57,997486257,boston,141,1929925399,2766849525,
...

[download]

Desired output csv: 

date,time,,device,ifIndex,Bps,
2001-08-10,18:15:00,boston,141,,
2001-08-10,18:18:12,boston,141,11649,
2001-08-10,18:21:23,boston,141,24969,
...

[download]

In reply to control+data structures for multi-line math on csv by ybiC

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