Python group values in 2d list from CSV

Question

I have the following CSV

BBCP1,Grey,2140,805EC0FFFFE2,0000000066
BBCP1,Test,2150,805EC0FFFFE2,0000000066
BBCP1,Test,2151,805EC0FFFFE1,0000000066
BBCP1,Centre,2141,805EC0FFFFE3,000000077
BBCP1,Yellow,2142,805EC0FFFFE3,000000077
BBCP1,Purple,2143,805EC0FFFFE3,000000077
BBCP1,Green,2144,805EC0FFFFE3,000000077
BBCP1,Pink,2145,805EC0FFFFE3,000000077

I'm reading this data in using

data = list(csv.reader(open(csvFile)))

I want to turn this data into a 2d array or equivilent and group by the value in the 4th column (the MAC address), preserving the order they were in in the original list. So it would look like

[(BBCP1,Grey,2140,805EC0FFFFE2,0000000066),(BBCP1,Test,2150,805EC0FFFFE2,0000000066)],
[(BBCP1,Test,2151,805EC0FFFFE1,0000000066)],
[(BBCP1,Centre,2141,805EC0FFFFE3,000000077),
(BBCP1,Yellow,2142,805EC0FFFFE3,000000077),
(BBCP1,Purple,2143,805EC0FFFFE3,000000077),
(BBCP1,Green,2144,805EC0FFFFE3,000000077),
(BBCP1,Pink,2145,805EC0FFFFE3,000000077)]

Hopefully i've displayed the array correctly and it makes sense.

I then need to loop the arrays to output the data to file. Which i'm pretty sure i'm ok with a nested for loop.

Thanks in advance for any help

Answer 1

use defaultdict to group the data (groupby would require sorting and would be unefficient / would kill the order), then print the sorted dictionary values (sorting isn't really necessary, it's just to stabilize the output):

import csv,collections

d = collections.defaultdict(list)

for row in csv.reader(txt):
    mac_address = row[3]
    d[mac_address].append(row)

print(sorted(d.values()))

resulting in:

[[['BBCP1', 'Centre', '2141', '805EC0FFFFE3', '000000077'],
  ['BBCP1', 'Yellow', '2142', '805EC0FFFFE3', '000000077'],
  ['BBCP1', 'Purple', '2143', '805EC0FFFFE3', '000000077'],
  ['BBCP1', 'Green', '2144', '805EC0FFFFE3', '000000077'],
  ['BBCP1', 'Pink', '2145', '805EC0FFFFE3', '000000077']],
 [['BBCP1', 'Grey', '2140', '805EC0FFFFE2', '0000000066'],
  ['BBCP1', 'Test', '2150', '805EC0FFFFE2', '0000000066']],
 [['BBCP1', 'Test', '2151', '805EC0FFFFE1', '0000000066']]]

sorting according to key (the mac address):

values = [v for _,v in sorted(d.items())]

yields:

[[['BBCP1', 'Test', '2151', '805EC0FFFFE1', '0000000066']],
 [['BBCP1', 'Grey', '2140', '805EC0FFFFE2', '0000000066'],
  ['BBCP1', 'Test', '2150', '805EC0FFFFE2', '0000000066']],
 [['BBCP1', 'Centre', '2141', '805EC0FFFFE3', '000000077'],
  ['BBCP1', 'Yellow', '2142', '805EC0FFFFE3', '000000077'],
  ['BBCP1', 'Purple', '2143', '805EC0FFFFE3', '000000077'],
  ['BBCP1', 'Green', '2144', '805EC0FFFFE3', '000000077'],
  ['BBCP1', 'Pink', '2145', '805EC0FFFFE3', '000000077']]]