遍历python中的list并获得给定元素的最大值

Question

I have a CSV file made like so:

business unit; employee id; name; tax code;
1; 50; JOE BLOGGS; 123456789
1; 51; JOE BLOGGS; 123456789
1; 52; JOE BLOGGS; 123456789
3; 53; JOE BLOGGS; 123456789
5; 54; JOE BLOGGS; 123456789

The tax code is unique while the business units and id may vary. Since the employee I need is always the last one, it being his most recent and thus active working position, how can I loop through this file and append ONLY the last row to the array? ( Edit: the last line or better the highest id referring to that particular person, there might be other employees in the file )

my code is:

for line in csv:
 l = [i.strip() for i in line.split(';')]
 if l[3] not in d:
  d.append(l[3])
  c.append(l[2])
  b.append(l[1])
  a.append(l[0])

this way I obtain as a result a list containing only the first record, how can I get the last one? Thank you!

Answer 1

If I understand well, you'd like to get the last record for each tax code . Try this,

d = dict() # key by `tax code`
for line in csv:
    l = [i.strip() for i in line.split(';')]

    d[l[3]] = l # update

lists = d.values()

If your file is grouped by tax code , use itertools.groupby ,

import csv
import operator
import itertools

with open(filename, 'r') as f:
    header = next(f, None)
    for key, group in itertools.groupby(f, key=operator.itemgetter(3)):
        last_line = list(group)[-1]

        print(last_line)
        5; 54; JOE BLOGGS; 123456789

---

Previous answer: read the last line from a csv file.

Way 1: Use csv.reader

skipinitialspace=True is used to get rid of whitespace following the delimiter ; .

import csv

with open(filename, 'r') as f:
    headers = next(f, None) # the header
    lists = [row for row in csv.reader(f, delimiter=';', skipinitialspace=True)]

    print(lists[-1])
    # Output
    ['5', '54', 'JOE BLOGGS', '123456789']

Way 2: Use collections.deque

import csv
import collections

with open(filename, 'r') as f:
    last_line = collections.deque(csv.reader(f), 1)[0][0]

    print(last_line)
    # Output
    5; 54; JOE BLOGGS; 123456789