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+# Copyright (c) 2019 Cisco and/or its affiliates.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module holding AvgStdevStats class."""
+
+import math
+
+
+class AvgStdevStats:
+ """Class for statistics which include average and stdev of a group.
+
+ Contrary to other stats types, adding values to the group
+ is computationally light without any caching.
+
+ Instances are only statistics, the data itself is stored elsewhere.
+ """
+
+ def __init__(self, size=0, avg=0.0, stdev=0.0):
+ """Construct the stats object by storing the values needed.
+
+ Each value has to be numeric.
+ The values are not sanitized depending on size, wrong initialization
+ can cause delayed math errors.
+
+ :param size: Number of values participating in this group.
+ :param avg: Population average of the participating sample values.
+ :param stdev: Population standard deviation of the sample values.
+ :type size: int
+ :type avg: float
+ :type stdev: float
+ """
+ self.size = size
+ self.avg = avg
+ self.stdev = stdev
+
+ def __str__(self):
+ """Return string with human readable description of the group.
+
+ :returns: Readable description.
+ :rtype: str
+ """
+ return f"size={self.size} avg={self.avg} stdev={self.stdev}"
+
+ def __repr__(self):
+ """Return string executable as Python constructor call.
+
+ :returns: Executable constructor call.
+ :rtype: str
+ """
+ return (
+ f"AvgStdevStats(size={self.size!r},avg={self.avg!r}"
+ f",stdev={self.stdev!r})"
+ )
+
+ @classmethod
+ def for_runs(cls, runs):
+ """Return new stats instance describing the sequence of runs.
+
+ If you want to append data to existing stats object,
+ you can simply use the stats object as the first run.
+
+ Instead of a verb, "for" is used to start this method name,
+ to signify the result contains less information than the input data.
+
+ Here, Run is a hypothetical abstract class, an union of float and cls.
+ Defining that as a real abstract class in Python 2 is too much hassle.
+
+ :param runs: Sequence of data to describe by the new metadata.
+ :type runs: Iterable[Union[float, cls]]
+ :returns: The new stats instance.
+ :rtype: cls
+ """
+ # Using Welford method to be more resistant to rounding errors.
+ # Adapted from code for sample standard deviation at:
+ # https://www.johndcook.com/blog/standard_deviation/
+ # The logic of plus operator is taken from
+ # https://www.johndcook.com/blog/skewness_kurtosis/
+ total_size = 0
+ total_avg = 0.0
+ moment_2 = 0.0
+ for run in runs:
+ if isinstance(run, (float, int)):
+ run_size = 1
+ run_avg = run
+ run_stdev = 0.0
+ else:
+ run_size = run.size
+ run_avg = run.avg
+ run_stdev = run.stdev
+ old_total_size = total_size
+ delta = run_avg - total_avg
+ total_size += run_size
+ total_avg += delta * run_size / total_size
+ moment_2 += run_stdev * run_stdev * run_size
+ moment_2 += delta * delta * old_total_size * run_size / total_size
+ if total_size < 1:
+ # Avoid division by zero.
+ return cls(size=0)
+ # TODO: Is it worth tracking moment_2 instead, and compute and cache
+ # stdev on demand, just to possibly save some sqrt calls?
+ total_stdev = math.sqrt(moment_2 / total_size)
+ ret_obj = cls(size=total_size, avg=total_avg, stdev=total_stdev)
+ return ret_obj