Remove Objects from python list

Question

a = [
    {
        "id" : 15,
        "name" : "abc"
    },
    {
        "id" : 16,
        "name" : "xyz"
    },
    {
        "id" : 17,
        "name" : "pqr"
    }
]

b = [15,17]

I have two lists as above, I want to remove the object from list a if its id is not present in list b. Any help, how to do that?

Output List:

[
    {
        "id" : 15,
        "name" : "abc"
    },
    {
        "id" : 17,
        "name" : "pqr"
    }
]

Possible duplicate of How to filter a dictionary according to an arbitrary condition function? — jpp
– jpp, Commented Feb 16, 2018 at 9:40
@cᴏʟᴅsᴘᴇᴇᴅ yes it works, have accepted the answer — usr_11
– usr_11, Commented Feb 19, 2018 at 11:31

cs95 · Accepted Answer · 2018-02-16 06:58:38Z

6

Iterate in reverse gear for efficient, in-place deletion. Convert b into a set for constant time lookup.

c = set(b)    
for i in reversed(range(len(a))):  # thanks to @juanpa.arrivillaga for this bit 
    if a[i]['id'] not in c:
        del a[i]

Otherwise, use a list comprehension and create it again:

a = [i for i in a if i['id'] in c]

print(a)
[{'id': 15, 'name': 'abc'}, {'id': 17, 'name': 'pqr'}]

edited Feb 16, 2018 at 6:58

answered Feb 16, 2018 at 6:01

cs95

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2 Comments

juanpa.arrivillaga Over a year ago

I've come to prefer reversed(range(len(a))) instead of range(len(a) - 1, -1, -1)

cs95 Over a year ago

@juanpa.arrivillaga Will commit that to memory! Very nifty.

akiva · Accepted Answer · 2018-02-16 06:01:49Z

0

use list comprehention hence:

[i for i in a if i['id']!=b[0] and i['name']!=b[1]]

answered Feb 16, 2018 at 6:01

akiva

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1 Comment

FatihAkici Over a year ago

I think your answer is wrong because b[0], b[1], and i['name'] are not relevant, and OP wants to keep those items whose ids are in b. So [i for i in a if i['id'] in b] might be what you are trying to say.

Mahesh Karia · Accepted Answer · 2018-02-16 08:46:12Z

0

You can use list comprehension as follows:

a = [
     {
        "id" : 15,
        "name" : "abc"
    },
    {
        "id" : 16,
        "name" : "xyz"
    },
    {
        "id" : 17,
        "name" : "pqr"
    }]

b = [15, 17]

print [a[_] for _ in xrange(len(a)) if a[_]["id"] in b]

output:

[{'id': 15, 'name': 'abc'}, {'id': 17, 'name': 'pqr'}]

answered Feb 16, 2018 at 8:46

Mahesh Karia

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