Pythonic way of getting a list of IDs from a dictionary

Question

Assuming I have the following data structure

theValues = [
  { "id": "123", "name": "foo" },
  { "id": "321", "name": "bar" },
  { "id": "231", "name": "baz" }
]

What's the best Pythonistic way to get a list of the IDs [123,321,231] ?

If this were javascript, I'd probably just use filter on each element in the list with an anonymous function, but I can't seem to find a Python equivalent. I know I could do the following:

myList = []
for v in theValues: myList.append(v["id"])

Ultimately, I'd like to reduce the list of dictionaries to a comma-separated list, which I suppose I could do with a join... though that syntax still looks weird to me. Is there a better way?

myListIds = ",".join( myList )

Is that the most common way of doing it? In PHP, I could do something like:

$myListIds = implode(",", array_map( values, function( v ) { return v["ID"]; } ));

How about `[d["id"] for d in values]`? Also, the variable name `values` shadows the name of the dict method. — hilberts_drinking_problem, Dec 02 '18 at 05:30
@YakymPirozhenko thanks... I'll change that var name for clarity. It was sample data so I wasn't thinking. — Armstrongest, Dec 02 '18 at 05:32

score 10 · Accepted Answer · answered Dec 02 '18 at 05:35

10

values = [
  { "id": "123", "name": "foo" },
  { "id": "321", "name": "bar" },
  { "id": "231", "name": "baz" }
]
ids = [val['id'] for val in values]
print(ids)

Based on this answer

answered Dec 02 '18 at 05:35

Sreeragh A R

2,871
3
27
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1

I'm interested in how this works. I'm going to look up this and the more on the lambda function. thx. – Armstrongest Dec 02 '18 at 05:41
Thank you for this answer. It let me down the path of list comprehensions and they are amazing. – Armstrongest Dec 12 '18 at 05:31

Jonathan Gagne · Answer 2 · 2018-12-02T07:11:33.127

4

There is a way to map with Python as well, see below the example.

values = [
  { "id": "123", "name": "foo" },
  { "id": "321", "name": "bar" },
  { "id": "231", "name": "baz" }
]

my_list = map(lambda x: x["id"], values)

print(my_list)

Output:

['123', '321', '231']

About the comma separated list, if you would like to have a string, you can use join as below to obtain it:

print(", ".join(my_list))

If you would like to make it in one line of code, here is how you should do it:

print(", ".join(map(lambda x: x["id"], values)))

Output:

123, 321, 231

edited Dec 02 '18 at 07:11

answered Dec 02 '18 at 05:25

Jonathan Gagne

4,241
5
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So could I also join using `",".join( list(map(lambda x: x["id"], values)) )` or is that too ugly? – Armstrongest Dec 02 '18 at 05:34
1

Seems pretty simple and human readable to me. – Jonathan Gagne Dec 02 '18 at 05:34
thanks. Looks like both answers approach this from similar but different paths. Need to look more into this. ^_^ – Armstrongest Dec 02 '18 at 05:42
1

You probably don't need to cast `list()`, `", ".join(map(lambda x: x["id"], values))` should be fine. – RoadRunner Dec 02 '18 at 06:03

Pythonic way of getting a list of IDs from a dictionary

2 Answers2