I have some kind of verbose logic that I'd like to compact down with some comprehensions.
Essentially, I have a dict object that I'm reading from which has 16 values in it that I'm concerned with. I'm getting the keys that I want with the following comprehension:
["I%d" % (i,) for i in range(16)]
The source dictionary kind of looks like this:
{ "I0": [0,1,5,2], "I1": [1,3,5,2], "I2": [5,9,10,1], ... }
I'd like to essentially map this dictionary to be something like this:
[
{ "I0": 0, "I1": 1, "I2": 5, ... }
{ "I0": 1, "I1": 3, "I2": 9, ... }
...
]
How can I map things with list and dictionary comprehensions to transform my source dict into my destination list of dictionaries?
This is a fully functional solution that can be applied on arbitrary size.
d = { "I0": [0,1,5,2], "I1": [1,3,5,2], "I2": [5,9,10,1]}
map(dict, zip(*map(lambda (k, v): map(lambda vv: (k, vv), v), d.iteritems())))
to elaborate: (I'm using ipython
and the underscore _
means the previous output)
In [1]: d = {'I0': [0, 1, 5, 2], 'I1': [1, 3, 5, 2], 'I2': [5, 9, 10, 1]}
In [2]: map(lambda (k, v): map(lambda vv: (k, vv), v), _.iteritems())
Out[2]:
[[('I1', 1), ('I1', 3), ('I1', 5), ('I1', 2)],
[('I0', 0), ('I0', 1), ('I0', 5), ('I0', 2)],
[('I2', 5), ('I2', 9), ('I2', 10), ('I2', 1)]]
In [3]: zip(*_)
Out[3]:
[(('I1', 1), ('I0', 0), ('I2', 5)),
(('I1', 3), ('I0', 1), ('I2', 9)),
(('I1', 5), ('I0', 5), ('I2', 10)),
(('I1', 2), ('I0', 2), ('I2', 1))]
In [4]: map(dict, _)
Out[4]:
[{'I0': 0, 'I1': 1, 'I2': 5},
{'I0': 1, 'I1': 3, 'I2': 9},
{'I0': 5, 'I1': 5, 'I2': 10},
{'I0': 2, 'I1': 2, 'I2': 1}]
How I would solve it:
Firstly, I would get for each key a list containing tuples, where the first item would be the key and the second one would be one of the values from the list:
>>> [ [ (k, i) for i in l] for k, l in d.items() ]
[[('I1', 1), ('I1', 3), ('I1', 5), ('I1', 2)],
[('I0', 0), ('I0', 1), ('I0', 5), ('I0', 2)],
[('I2', 5), ('I2', 9), ('I2', 10), ('I2', 1)]]
Then I would transverse this list, creating a list of tuples containing each corresponding key, using the zip function:
>>> list(zip(*[ [ (k, i) for i in l] for k, l in d.items() ]))
[(('I1', 1), ('I0', 0), ('I2', 5)),
(('I1', 3), ('I0', 1), ('I2', 9)),
(('I1', 5), ('I0', 5), ('I2', 10)),
(('I1', 2), ('I0', 2), ('I2', 1))]
These sublists can passed as parameter to the dict constructor:
>>> [dict(lp) for lp in zip(*[ [ (k, i) for i in l] for k, l in d.items() ])]
[{'I0': 0, 'I1': 1, 'I2': 5},
{'I0': 1, 'I1': 3, 'I2': 9},
{'I0': 5, 'I1': 5, 'I2': 10},
{'I0': 2, 'I1': 2, 'I2': 1}]
In practice, however, I would never recommend one to do such a thing in one line only:
>>> pairs = [ [ (k, i) for i in l] for k, l in d.items() ]
>>> transversed = zip(*pairs)
>>> ds = [dict(t) for t in transversed]
>>> pprint(ds)
[{'I0': 0, 'I1': 1, 'I2': 5},
{'I0': 1, 'I1': 3, 'I2': 9},
{'I0': 5, 'I1': 5, 'I2': 10},
{'I0': 2, 'I1': 2, 'I2': 1}]
Actually, I would say I posted this answer mostly to suggest you to split your solution in more than one line.
There is short and easy solution:
keys = data.keys()
values = data.values()
transformed = [dict(zip(keys, t)) for t in zip(*values)]
The key here is transposing values matrix, which is done with zip(*values)
, then we just reconstruct dicts.
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