Python equivalent of PHP array_column

Question

In PHP I use the array_column() function a lot as it allows me to retrieve values from a specific column inside an array returned themselves in a nice array, for example, using this array:

$users = [
    [
        'id' => 1,
        'name' => 'Peter'
    ],
    [
        'id' => 2,
        'name' => 'Paul'
    ],
    [
        'id' => 3,
        'name' => 'John'
    ]
];

Doing array_column($users, 'name') will return:

Array
(
    [0] => Peter
    [1] => Paul
    [2] => John
)

Since transitioning to Python I still haven't found a built in function that I can use to do the same thing on a list of dicts for example.

Does such a function exist and if not, what is the best way to achieve this?

Peter Featherstone · Accepted Answer · 2017-08-01 16:17:01Z

6

You can use a list comprehension to extract the 'column' of interest. There is no direct Python function to my knowledge. List comprehensions are almost always faster than using map. Python List Comprehension Vs. Map

users = [
    {
        'id': 1,
        'name': 'Peter'
    },
    {
        'id': 2,
        'name': 'Paul'
    },
    {
        'id': 3,
        'name': 'John'
    }
]

>>> [(user.get('id'), user.get('name')) for user in users]
[(1, 'Peter'), (2, 'Paul'), (3, 'John')]

Or using an enumerated index location instead of the id field:

>>> [(n, user.get('name')) for n, user in enumerate(users)]
[(0, 'Peter'), (1, 'Paul'), (2, 'John')]

Or just the names...

>>> [user.get('name') for user in users]
['Peter', 'Paul', 'John']

edited Aug 1, 2017 at 16:17

Peter Featherstone

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answered Aug 1, 2017 at 16:02

Alexander

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Comments

Alexander Ejbekov · Accepted Answer · 2017-08-01 16:00:10Z

1

Something like this?

arr = [
        {
        'id' : 1,
        'name' : 'Peter'
        },
    {
        'id' : 2,
        'name' : 'Paul'
    },
    {
        'id' : 3,
        'name' : 'John'
    }
]
list(map(lambda x: x["name"], arr))

answered Aug 1, 2017 at 16:00

Alexander Ejbekov

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4 Comments

Peter Featherstone Over a year ago

That definitely does the job but I'm assuming this means there is no built in function such as array_column that does this all behind the scenes?

juanpa.arrivillaga Over a year ago

@PeterFeatherstone no, there isn't. A "list of dicts" is your own, composite data-structure. You have to deal with it explicitly. Also, while people tend to use list-of-dicts quite often, I think it is almost always better to use a list of namedtuples.

Peter Featherstone Over a year ago

@juanpa.arrivillaga Fair point and thanks for the explanation :-)

juanpa.arrivillaga Over a year ago

@PeterFeatherstone Note, I would say list-comprehensions are favored over list(map(...)) unless the function you are mapping is a built-in, something like map(int, list_of_number_strings)

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