ubelt.util_dict module

Functions for working with dictionaries.

The dict_hist() function counts the number of discrete occurrences of hashable items. Similarly find_duplicates() looks for indices of items that occur more than k=1 times.

The map_keys() and map_vals() functions are useful for transforming the keys and values of a dictionary with less syntax than a dict comprehension.

The dict_union(), dict_isect(), and dict_subset() functions are similar to the set equivalents.

The dzip() function zips two iterables and packs them into a dictionary where the first iterable is used to generate keys and the second generates values.

The group_items() function takes two lists and returns a dict mapping values in the second list to all items in corresponding locations in the first list.

The invert_dict() function swaps keys and values. See the function docs for details on dealing with unique and non-unique values.

The ddict() and odict() functions are alias for the commonly used collections.defaultdict() and collections.OrderedDict() classes.

ubelt.util_dict.odict

alias of collections.OrderedDict

ubelt.util_dict.ddict

alias of collections.defaultdict

class ubelt.util_dict.AutoDict[source]

Bases: dict

An infinitely nested default dict of dicts.

Implementation of Perl’s autovivification feature.

SeeAlso:
AutoOrderedDict - the ordered version

References

[1]http://stackoverflow.com/questions/651794/init-dict-of-dicts

Example

>>> import ubelt as ub
>>> auto = ub.AutoDict()
>>> auto[0][10][100] = None
>>> assert str(auto) == '{0: {10: {100: None}}}'
to_dict()[source]

Recursively casts a AutoDict into a regular dictionary. All nested AutoDict values are also converted.

Returns:a copy of this dict without autovivification
Return type:dict

Example

>>> from ubelt.util_dict import AutoDict
>>> auto = AutoDict()
>>> auto[1] = 1
>>> auto['n1'] = AutoDict()
>>> static = auto.to_dict()
>>> assert not isinstance(static, AutoDict)
>>> assert not isinstance(static['n1'], AutoDict)
class ubelt.util_dict.AutoOrderedDict[source]

Bases: collections.OrderedDict, ubelt.util_dict.AutoDict

An infinitely nested default dict of dicts that maintains the ordering of items.

SeeAlso:
AutoDict - the unordered version of this class

Example

>>> import ubelt as ub
>>> auto = ub.AutoOrderedDict()
>>> auto[0][3] = 3
>>> auto[0][2] = 2
>>> auto[0][1] = 1
>>> assert list(auto[0].values()) == [3, 2, 1]
ubelt.util_dict.dzip(items1, items2, cls=<class 'dict'>)[source]

Zips elementwise pairs between items1 and items2 into a dictionary. Values from items2 can be broadcast onto items1.

Parameters:
  • items1 (Iterable) – full sequence
  • items2 (Iterable) – can either be a sequence of one item or a sequence of equal length to items1
  • cls (Type[dict], default=dict) – dictionary type to use.
Returns:

similar to dict(zip(items1, items2)).

Return type:

dict

Example

>>> assert dzip([1, 2, 3], [4]) == {1: 4, 2: 4, 3: 4}
>>> assert dzip([1, 2, 3], [4, 4, 4]) == {1: 4, 2: 4, 3: 4}
>>> assert dzip([], [4]) == {}
ubelt.util_dict.group_items(items, groupids)[source]

Groups a list of items by group id.

Parameters:
  • items (Iterable) – a list of items to group
  • groupids (Iterable or Callable) – a corresponding list of item groupids or a function mapping an item to a groupid.
Returns:

groupid_to_items: maps a groupid to a list of items

Return type:

dict

CommandLine:
python -m ubelt.util_dict group_items

Example

>>> import ubelt as ub
>>> items    = ['ham',     'jam',   'spam',     'eggs',    'cheese', 'banana']
>>> groupids = ['protein', 'fruit', 'protein',  'protein', 'dairy',  'fruit']
>>> groupid_to_items = ub.group_items(items, groupids)
>>> print(ub.repr2(groupid_to_items, nl=0))
{'dairy': ['cheese'], 'fruit': ['jam', 'banana'], 'protein': ['ham', 'spam', 'eggs']}
ubelt.util_dict.dict_hist(item_list, weight_list=None, ordered=False, labels=None)[source]

Builds a histogram of items, counting the number of time each item appears in the input.

Parameters:
  • item_list (Iterable) – hashable items (usually containing duplicates)
  • weight_list (Iterable, default=None) – Corresponding weights for each item.
  • ordered (bool, default=False) – If True the result is ordered by frequency.
  • labels (Iterable, default=None) – Expected labels. Allows this function to pre-initialize the histogram. If specified the frequency of each label is initialized to zero and item_list can only contain items specified in labels.
Returns:

dictionary where the keys are items in item_list, and the values

are the number of times the item appears in item_list.

Return type:

dict

CommandLine:
python -m ubelt.util_dict dict_hist

Example

>>> import ubelt as ub
>>> item_list = [1, 2, 39, 900, 1232, 900, 1232, 2, 2, 2, 900]
>>> hist = ub.dict_hist(item_list)
>>> print(ub.repr2(hist, nl=0))
{1: 1, 2: 4, 39: 1, 900: 3, 1232: 2}

Example

>>> import ubelt as ub
>>> item_list = [1, 2, 39, 900, 1232, 900, 1232, 2, 2, 2, 900]
>>> hist1 = ub.dict_hist(item_list)
>>> hist2 = ub.dict_hist(item_list, ordered=True)
>>> try:
>>>     hist3 = ub.dict_hist(item_list, labels=[])
>>> except KeyError:
>>>     pass
>>> else:
>>>     raise AssertionError('expected key error')
>>> #result = ub.repr2(hist_)
>>> weight_list = [1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1]
>>> hist4 = ub.dict_hist(item_list, weight_list=weight_list)
>>> print(ub.repr2(hist1, nl=0))
{1: 1, 2: 4, 39: 1, 900: 3, 1232: 2}
>>> print(ub.repr2(hist4, nl=0))
{1: 1, 2: 4, 39: 1, 900: 1, 1232: 0}
ubelt.util_dict.find_duplicates(items, k=2, key=None)[source]

Find all duplicate items in a list.

Search for all items that appear more than k times and return a mapping from each (k)-duplicate item to the positions it appeared in.

Parameters:
  • items (Iterable) – hashable items possibly containing duplicates
  • k (int, default=2) – only return items that appear at least k times.
  • key (Callable, default=None) – Returns indices where key(items[i]) maps to a particular value at least k times.
Returns:

maps each duplicate item to the indices at which it appears

Return type:

dict

Example

>>> import ubelt as ub
>>> items = [0, 0, 1, 2, 3, 3, 0, 12, 2, 9]
>>> duplicates = ub.find_duplicates(items)
>>> # Duplicates are a mapping from each item that occurs 2 or more
>>> # times to the indices at which they occur.
>>> assert duplicates == {0: [0, 1, 6], 2: [3, 8], 3: [4, 5]}
>>> # You can set k=3 if you want to don't mind duplicates but you
>>> # want to find triplicates or quadruplets etc.
>>> assert ub.find_duplicates(items, k=3) == {0: [0, 1, 6]}

Example

>>> import ubelt as ub
>>> items = [0, 0, 1, 2, 3, 3, 0, 12, 2, 9]
>>> # note: k can less then 2
>>> duplicates = ub.find_duplicates(items, k=0)
>>> print(ub.repr2(duplicates, nl=0))
{0: [0, 1, 6], 1: [2], 2: [3, 8], 3: [4, 5], 9: [9], 12: [7]}

Example

>>> import ubelt as ub
>>> items = [10, 11, 12, 13, 14, 15, 16]
>>> duplicates = ub.find_duplicates(items, key=lambda x: x // 2)
>>> print(ub.repr2(duplicates, nl=0))
{5: [0, 1], 6: [2, 3], 7: [4, 5]}
ubelt.util_dict.dict_subset(dict_, keys, default=NoParam)[source]

Get a subset of a dictionary

Parameters:
  • dict_ (Mapping) – superset dictionary
  • keys (Iterable) – keys to take from dict_
  • default (object, optional) – if specified uses default if keys are missing
Returns:

subset dictionary

Return type:

OrderedDict

SeeAlso:
dict_isect() - similar functionality, but will only take existing
keys

Example

>>> import ubelt as ub
>>> dict_ = {'K': 3, 'dcvs_clip_max': 0.2, 'p': 0.1}
>>> keys = ['K', 'dcvs_clip_max']
>>> subdict_ = ub.dict_subset(dict_, keys)
>>> print(ub.repr2(subdict_, nl=0))
{'K': 3, 'dcvs_clip_max': 0.2}
ubelt.util_dict.dict_union(*args)[source]

Combines the disjoint keys in multiple dictionaries. For intersecting keys, dictionaries towards the end of the sequence are given precedence.

Parameters:*args – a sequence of dictionaries
Returns:OrderedDict if the first argument is an OrderedDict, otherwise dict
Return type:Dict | OrderedDict
SeeAlso:
collections.ChainMap() - a standard python builtin data structure that provides a view that treats multiple dicts as a single dict. https://docs.python.org/3/library/collections.html#chainmap-objects

Example

>>> result = dict_union({'a': 1, 'b': 1}, {'b': 2, 'c': 2})
>>> assert result == {'a': 1, 'b': 2, 'c': 2}
>>> dict_union(odict([('a', 1), ('b', 2)]), odict([('c', 3), ('d', 4)]))
OrderedDict([('a', 1), ('b', 2), ('c', 3), ('d', 4)])
>>> dict_union()
{}
ubelt.util_dict.dict_diff(*args)[source]

Constructs a dictionary that contains any of the keys in the first arg, which are not in any of the following args.

Parameters:*args – a sequence of dictionaries (or sets of keys)
Returns:OrderedDict if the first argument is an OrderedDict, otherwise dict
Return type:Dict | OrderedDict

Example

>>> dict_diff({'a': 1, 'b': 1}, {'a'}, {'c'})
{'b': 1}
>>> dict_diff(odict([('a', 1), ('b', 2)]), odict([('c', 3)]))
OrderedDict([('a', 1), ('b', 2)])
>>> dict_diff()
{}
>>> dict_diff({'a': 1, 'b': 2}, {'c'})
ubelt.util_dict.dict_isect(*args)[source]

Constructs a dictionary that contains keys common between all inputs. The returned values will only belong to the first dictionary.

Parameters:*args – a sequence of dictionaries (or sets of keys)
Returns:OrderedDict if the first argument is an OrderedDict, otherwise dict
Return type:Dict | OrderedDict

Notes

This function can be used as an alternative to dict_subset() where any key not in the dictionary is ignored. See the following example:

>>> dict_isect({'a': 1, 'b': 2, 'c': 3}, ['a', 'c', 'd'])
{'a': 1, 'c': 3}

Example

>>> dict_isect({'a': 1, 'b': 1}, {'b': 2, 'c': 2})
{'b': 1}
>>> dict_isect(odict([('a', 1), ('b', 2)]), odict([('c', 3)]))
OrderedDict()
>>> dict_isect()
{}
ubelt.util_dict.map_vals(func, dict_)[source]

Apply a function to every value in a dictionary.

Creates a new dictionary with the same keys and modified values.

Parameters:
  • func (callable | indexable) – a function or indexable object
  • dict_ (dict) – a dictionary
Returns:

transformed dictionary

Return type:

dict

Example

>>> dict_ = {'a': [1, 2, 3], 'b': []}
>>> newdict = map_vals(len, dict_)
>>> assert newdict ==  {'a': 3, 'b': 0}

Example

>>> # Can also use an indexable as ``func``
>>> dict_ = {'a': 0, 'b': 1}
>>> func = [42, 21]
>>> newdict = map_vals(func, dict_)
>>> assert newdict ==  {'a': 42, 'b': 21}
>>> print(newdict)
ubelt.util_dict.map_keys(func, dict_)[source]

Apply a function to every key in a dictionary.

Creates a new dictionary with the same values and modified keys. An error is raised if the new keys are not unique.

Parameters:
  • func (callable | indexable) – a function or indexable object
  • dict_ (dict) – a dictionary
Returns:

transformed dictionary

Return type:

dict

Raises:

Exception – if multiple keys map to the same value

Example

>>> dict_ = {'a': [1, 2, 3], 'b': []}
>>> func = ord
>>> newdict = map_keys(func, dict_)
>>> print(newdict)
>>> assert newdict == {97: [1, 2, 3], 98: []}
>>> dict_ = {0: [1, 2, 3], 1: []}
>>> func = ['a', 'b']
>>> newdict = map_keys(func, dict_)
>>> print(newdict)
>>> assert newdict == {'a': [1, 2, 3], 'b': []}
ubelt.util_dict.invert_dict(dict_, unique_vals=True)[source]

Swaps the keys and values in a dictionary.

Parameters:
  • dict_ (dict) – dictionary to invert
  • unique_vals (bool, default=True) – if False, the values of the new dictionary are sets of the original keys.
Returns:

inverted

Return type:

dict

Notes

The must values be hashable.

If the original dictionary contains duplicate values, then only one of the corresponding keys will be returned and the others will be discarded. This can be prevented by setting unique_vals=True, causing the inverted keys to be returned in a set.

Example

>>> import ubelt as ub
>>> dict_ = {'a': 1, 'b': 2}
>>> inverted = ub.invert_dict(dict_)
>>> assert inverted == {1: 'a', 2: 'b'}

Example

>>> import ubelt as ub
>>> dict_ = ub.odict([(2, 'a'), (1, 'b'), (0, 'c'), (None, 'd')])
>>> inverted = ub.invert_dict(dict_)
>>> assert list(inverted.keys())[0] == 'a'

Example

>>> import ubelt as ub
>>> dict_ = {'a': 1, 'b': 0, 'c': 0, 'd': 0, 'f': 2}
>>> inverted = ub.invert_dict(dict_, unique_vals=False)
>>> assert inverted == {0: {'b', 'c', 'd'}, 1: {'a'}, 2: {'f'}}