def find_histogram_params(num_buckets, min_value, max_value, multiplier):
"""
Compute the parameters to use for the histogram. Using the provided
arguments, ensure that the generated histogram encapsolates the desired range.
:param int num_buckets: The number of buckets the histogram should contain.
:param float min_value: The minimum value allowed to be in the histogram inclusive.
:param float max_value: The maximum value allowed to be in the histogram inclusive.
:param int multipler: The multiplier we should use to preserve the desired precision.
"""
scaled_min = 0 if min_value is None else multiplier * min_value
scaled_max = 0 if max_value is None else multiplier * max_value
# align the first bin with the minimum value
start_offset = int(scaled_min)
# finding the bounds might result in None if there isn't sufficient data
if min_value is None or max_value is None:
return HistogramParams(num_buckets, 1, start_offset, multiplier)
bucket_size = nice_int((scaled_max - scaled_min) / float(num_buckets))
if bucket_size == 0:
bucket_size = 1
# adjust the first bin to a nice value
start_offset = int(scaled_min / bucket_size) * bucket_size
# Sometimes the max value lies on the bucket boundary, and since the end
# of the bucket is exclusive, it gets excluded. To account for that, we
# increase the width of the buckets to cover the max value.
if start_offset + num_buckets * bucket_size <= scaled_max:
bucket_size = nice_int(bucket_size + 1)
# compute the bin for max value and adjust the number of buckets accordingly
# to minimize unnecessary empty bins at the tail
last_bin = int(
(scaled_max - start_offset) / bucket_size) * bucket_size + start_offset
num_buckets = (last_bin - start_offset) // bucket_size + 1
return HistogramParams(num_buckets, bucket_size, start_offset, multiplier)
def test_nice_int():
specs = [
(0, 1, 0),
(1, 2, 1),
(2, 3, 2),
(3, 6, 5),
(6, 11, 10),
(11, 21, 20),
(21, 26, 25),
(26, 51, 50),
(51, 101, 100),
(101, 121, 120),
(121, 201, 200),
(201, 251, 250),
(251, 501, 500),
(501, 751, 750),
(751, 1001, 1000),
(1001, 1201, 1200),
(1201, 2001, 2000),
(2001, 2501, 2500),
(2501, 5001, 5000),
(5001, 7501, 7500),
(7501, 10001, 10000),
(10001, 12001, 12000),
(12001, 20001, 20000),
(20001, 25001, 25000),
(25001, 50001, 50000),
(50001, 75001, 75000),
(75001, 100001, 100000),
]
for start, stop, expected in specs:
for x in range(start, stop):
assert nice_int(x) == expected, "{} was rounded to {}, not {}".format(
x, nice_int(x), expected
)
assert nice_int(-x) == -expected, "{} was rounded to {}, not {}".format(
-x, nice_int(-x), -expected
)