Subtracting list along with duplicates in python

Question

I have two lists:

l1=['TUDCAPL.CLM_NUM_CD',
    'TUDCAPL.CRT_TS',
    'TUDCAPL.CLM_NUM_CD',
    'TUDCAPL.CRT_TS',
    'TUDCAPJ.CLM_NUM_CD',
    'TUDCAPJ.CRT_TS']

l2 = ['TUDCAPL.CLM_NUM_CD',
      'TUDCAPL.CRT_TS']

I want my result to be

l3 = ['TUDCAPL.CLM_NUM_CD',
      'TUDCAPL.CRT_TS',
      'TUDCAPJ.CLM_NUM_CD',
      'TUDCAPJ.CRT_TS']

I used l3 = [x for x in l1 if x not in l2] but the result is ['TUDCAPJ.CLM_NUM_CD','TUDCAPJ.CRT_TS'] ignoring the duplicates. How can I get the duplicates along with other unique values?

Will there are situations when `l2` contains something that is not in `l1`? — Tai, Jan 14 '18 at 13:06

score 2 · Accepted Answer · edited Jan 15 '18 at 01:37

Copy the list (if you do not want to change l1). Loop once over the items in l2 and remove it from the new list. The remove function will discard the first occurrence of each item, leaving the others and the order unaffected.

l1 = ['TUDCAPL.CLM_NUM_CD',
      'TUDCAPL.CRT_TS',
      'TUDCAPL.CLM_NUM_CD',
      'TUDCAPL.CRT_TS',
      'TUDCAPJ.CLM_NUM_CD',
      'TUDCAPJ.CRT_TS']

l2 = ['TUDCAPL.CLM_NUM_CD',
      'TUDCAPL.CRT_TS']

l3 = list(l1)
for x in l2:
    if x in l3:
        l3.remove(x)

from pprint import pprint
pprint(l3)

Result:

['TUDCAPL.CLM_NUM_CD', 
 'TUDCAPL.CRT_TS', 
 'TUDCAPJ.CLM_NUM_CD', 
 'TUDCAPJ.CRT_TS']

score 1 · Answer 2 · answered Jan 14 '18 at 11:04

1

You can use a set:

l3 = set(l1)
l3.update(l2)
print l3

answered Jan 14 '18 at 11:04

Jordan

1,375
14
17

order isnt maintained :-( – lpdd Jan 14 '18 at 11:27
Look for OrderedSet – Jordan Jan 14 '18 at 11:29
this might help https://stackoverflow.com/questions/1653970/does-python-have-an-ordered-set – Manoj Kengudelu Jan 14 '18 at 12:05
What if the number of duplicates is more than 2. Say l1= [2, 2, 2] and l2 =[2]. – Tai Jan 14 '18 at 13:14

score 0 · Answer 3 · answered Jan 14 '18 at 11:35

I know it's not the best solution but it will keep the order and the unique elements of your list:

from collections import OrderedDict

l1=['TUDCAPL.CLM_NUM_CD',
    'TUDCAPL.CRT_TS',
    'TUDCAPL.CLM_NUM_CD',
    'TUDCAPL.CRT_TS',
    'TUDCAPJ.CLM_NUM_CD',
    'TUDCAPJ.CRT_TS']

l2 = ['TUDCAPL.CLM_NUM_CD',
      'TUDCAPL.CRT_TS']


d = OrderedDict(zip(l1,[None]*len(l1)))
d2 = OrderedDict(zip(l2,[None]*len(l2)))

d.update(d2)
print(d.keys()) # this will contain the resulting list of strings

score -1 · Answer 4 · edited Jan 14 '18 at 11:26

-1

Try to copy your list to a set (this way you get unique values):

l1 = ['TUDCAPL.CLM_NUM_CD', 
      'TUDCAPL.CRT_TS',
      'TUDCAPL.CLM_NUM_CD', 
      'TUDCAPL.CRT_TS', 
      'TUDCAPJ.CLM_NUM_CD', 
      'TUDCAPJ.CRT_TS']
s1 = set(l1)
print(s1)

edited Jan 14 '18 at 11:26

Michael H.

3,323
2
23
31

answered Jan 14 '18 at 11:04

Jay Shankar Gupta

5,918
1
10
27

This removes the duplicates. They should be preserved. – Jongware Jan 14 '18 at 11:35
why you want to preserve the duplicate values if want go for dictionary and maintain there count in value – Jay Shankar Gupta Jan 14 '18 at 11:39
It's the OP's requirement, not mine. – Jongware Jan 14 '18 at 11:45

Subtracting list along with duplicates in python

4 Answers4