Removing entries from a dictionary based on values

Question

I have a dictionary with character-integer key-value pair. I want to remove all those key value pairs where the value is 0.

For example:

>>> hand
{'a': 0, 'i': 0, 'm': 1, 'l': 1, 'q': 0, 'u': 0}

I want to reduce the same dictionary to this:

>>> hand
{'m': 1, 'l': 1}

Is there an easy way to do that?

see this..http://stackoverflow.com/questions/5447494/best-way-to-remove-an-item-from-a-python-dictionary — Ankit Chauhan, Mar 01 '13 at 13:15

Niklas B. · Accepted Answer · 2014-08-28T15:36:33.527

37

You can use a dict comprehension:

>>> { k:v for k, v in hand.items() if v }
{'m': 1, 'l': 1}

Or, in pre-2.7 Python, the dict constructor in combination with a generator expression:

>>> dict((k, v) for k, v in hand.iteritems() if v)
{'m': 1, 'l': 1}

edited Aug 28 '14 at 15:36

answered Mar 01 '13 at 13:13

Niklas B.

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Note that this removes all values that evaluate to `False`. This is subtly different if you have non-integer values as well. – Gareth Latty Mar 01 '13 at 13:24
@Lattyware: It looks to me like OP only has integers as values... I can only work with what I get :) – Niklas B. Mar 01 '13 at 13:37
using `.items` instead of `.iteritems` can be very inefficient for larger data sets. – Don Aug 28 '14 at 14:24
@Don that depends on the version of Python you use. I'm usually assuming the newest version unless otherwise specified. Agreed though for my second example – Niklas B. Aug 28 '14 at 15:35
@NiklasB. Thanks for the info, I spend so much time in 2.7 I actually didn't know about that change. Good stuff – Don Sep 02 '14 at 13:24

score 13 · Answer 2 · edited Jul 01 '17 at 00:52

13

If you don't want to create a new dictionary, you can use this:

>>> hand = {'a': 0, 'i': 0, 'm': 1, 'l': 1, 'q': 0, 'u': 0}
>>> for key in list(hand.keys()):  ## creates a list of all keys
...     if hand[key] == 0:
...             del hand[key]
... 
>>> hand
{'m': 1, 'l': 1}
>>>

edited Jul 01 '17 at 00:52

R7L208

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answered Mar 01 '13 at 13:20

Fabian

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This is not allowed in Python 3: `Traceback (most recent call last): File "", line 1, in RuntimeError: dictionary changed size during iteration` – bugmenot123 Apr 29 '16 at 13:07
7

@bugmenot123 try `for key in list(hand.keys()):` – Fabian Apr 30 '16 at 18:49
Thank you! I ended up with that solution myself but had forgotten I posted here. :) – bugmenot123 Apr 30 '16 at 20:57
1

You can use `list(hand)`, no need to explicitly call `dict.keys()`. – Martijn Pieters Aug 09 '19 at 08:00

Volatility · Answer 3 · 2013-03-01T13:18:06.140

11

hand = {k: v for k, v in hand.iteritems() if v != 0}

For Pre-Python 2.7:

hand = dict((k, v) for k, v in hand.iteritems() if v != 0)

In both cases you're filtering out the keys whose values are 0, and assigning hand to the new dictionary.

edited Mar 01 '13 at 13:18

answered Mar 01 '13 at 13:13

Volatility

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IMO: better than Niklas' answer due to use of `iteritems` – Don Aug 28 '14 at 14:25

score 4 · Answer 4 · answered Mar 01 '13 at 13:12

4

A dict comprehension?

{k: v for k, v in hand.items() if v != 0}

In python 2.6 and earlier:

dict((k, v) for k, v in hand.items() if v != 0)

answered Mar 01 '13 at 13:12

Pavel Anossov

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Removing entries from a dictionary based on values

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