On 12/20/17 5:05 AM, Paul Moore wrote:
On 20 December 2017 at 03:09, Joel Croteau <[email protected]> wrote:
Well here is some code I wrote recently to build a histogram over a weighted
graph, before becoming aware that Counter existed (score is a float here):
from collections import defaultdict
total_score_by_depth = defaultdict(float)
total_items_by_depth = defaultdict(int)
num_nodes_by_score = defaultdict(int)
num_nodes_by_log_score = defaultdict(int)
num_edges_by_score = defaultdict(int)
for state in iter_graph_components():
try:
# There is probably some overlap here
ak = state['ak']
_, c = ak.score_paths(max_depth=15)
for edge in state['graph'].edges:
num_edges_by_score[np.ceil(20.0 * edge.score) / 20.0] += 1
for node in c.nodes:
total_score_by_depth[node.depth] += node.score
total_items_by_depth[node.depth] += 1
num_nodes_by_score[np.ceil(20.0 * node.score) / 20.0] += 1
num_nodes_by_log_score[np.ceil(-np.log10(node.score))] += 1
num_nodes_by_score[0.0] += len(state['graph'].nodes) - len(c.nodes)
num_nodes_by_log_score[100.0] += len(state['graph'].nodes) -
len(c.nodes)
except MemoryError:
print("Skipped massive.")
Without going too much into what this does, note that I could replace the
other defaultdicts with Counters, but I can't do the same thing with a
total_score_by_depth, at least not without violating the API.
Hmm, OK. I can't see any huge benefit from switching to a Counter,
though. You're not using any features of a Counter that aren't shared
by a defaultdict, nor is there any code here that could be simplified
or replaced by using such features...
I would
suggest that with a name like Counter, treating a class like a Counter
should be the more common use case. If it's meant to be a multiset, we
should call it a Multiset.
Personally, I consider "counting" to be something we do with integers
(whole numbers), not with floats. So for me the name Counter clearly
implies an integer. Multiset would be a reasonable alternative name,
but Python has a tradition of using "natural language" names over
"computer science" names, so I'm not surprised Counter was chosen
instead.
I guess it's ultimately a matter of opinion whether a float-based
Counter is a natural extension or not.
One thing to note is that Counter supports negative numbers, so we are
already outside the natural numbers :)
Python 3.6.4 (default, Dec 19 2017, 08:11:42)
>>> from collections import Counter
>>> c = Counter(a=4, b=2, c=0, d=-2)
>>> d = Counter(a=1, b=2, c=3, d=4)
>>> c.subtract(d)
>>> c
Counter({'a': 3, 'b': 0, 'c': -3, 'd': -6})
>>> list(c.elements())
['a', 'a', 'a']
--Ned.
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