Cleanup of page_measurement_results object

tools/telemetry/telemetry/value/merge_values.py

+# Copyright (c) 2013 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+def MergeLikeValuesFromSamePage(all_values):
+  """Merges values that measure the same thing on the same page.
+
+  A page may end up being measured multiple times, meaning that we may end up
+  with something like this:
+       ScalarValue(page1, 'x', 1)
+       ScalarValue(page2, 'x', 4)
+       ScalarValue(page1, 'x', 2)
+       ScalarValue(page2, 'x', 5)
+
+  This function will produce:
+       ListOfScalarValues(page1, 'x', [1, 2])
+       ListOfScalarValues(page2, 'x', [4, 5])
+
+  The workhorse of this code is Value.MergeLikeValuesFromSamePage.
+
+  This requires (but assumes) that the values passed in with the same grouping
+  key pass the Value.IsMergableWith test. If this is not obeyed, the
+  results will be undefined.
+  """
+  return _MergeLikeValuesCommon(
+      all_values,
+      lambda x: (x.page, x.name),
+      lambda v0, merge_group: v0.MergeLikeValuesFromSamePage(merge_group))
+
+
+def MergeLikeValuesFromDifferentPages(all_values, group_by_name_suffix=False):
+  """Merges values that measure the same thing on different pages.
+
+  After using MergeLikeValuesFromSamePage, one still ends up with values from
+  different pages:
+       ScalarValue(page1, 'x', 1)
+       ScalarValue(page1, 'y', 30)
+       ScalarValue(page2, 'x', 2)
+       ScalarValue(page2, 'y', 40)
+
+  This function will group the values of the same value_name together:
+       ListOfScalarValues(None, 'x', [1, 2])
+       ListOfScalarValues(None, 'y', [30, 40])
+
+  If group_by_name_suffix is True, then x.z and y.z are considered to be the
+  same value and are grouped together. If false, then x.z and y.z are
+  considered different.
+
+  The workhorse of this code is Value.MergeLikeValuesFromDifferentPages.
+
+  Not all values that go into this function will come out: not every value can
+  be merged across pages. Values whose MergeLikeValuesFromDifferentPages returns
+  None will be omitted from the results.
+
+  This requires (but assumes) that the values passed in with the same name pass
+  the Value.IsMergableWith test. If this is not obeyed, the results
+  will be undefined.
+  """
+  if group_by_name_suffix:
+    def key(value):
+      return value.name_suffix
+  else:
+    key = lambda x: x.name
+  return _MergeLikeValuesCommon(
+      all_values,
+      key,
+      lambda v0, merge_group: v0.MergeLikeValuesFromDifferentPages(
+          merge_group, group_by_name_suffix=group_by_name_suffix))
+
+
+def _MergeLikeValuesCommon(all_values, key_func, merge_func):
+  """Groups all_values by key_func then applies merge_func to the groups.
+
+  This takes the all_values list and groups each item in that using the key
+  provided by key_func. This produces groups of values with like keys. Thes are
+  then handed to the merge_func to produce a new key. If merge_func produces a
+  non-None return, it is added to the list of returned values.
+  """
+  # When merging, we want to merge values in a consistent order, e.g. so that
+  # Scalar(1), Scalar(2) predictably produces ListOfScalarValues([1,2]) rather
+  # than 2,1.
+  #
+  # To do this, the values are sorted by key up front. Then, grouping is
+  # performed using a dictionary, but as new groups are found, the order in
+  # which they were found is also noted.
+  #
+  # Merging is then performed on groups in group-creation-order. This ensures
+  # that the returned array is in a stable order, group by group.
+  #
+  # Within a group, the order is stable because of the original sort.
+  all_values = list(all_values)
+  merge_groups = GroupStably(all_values, key_func)
+
+  res = []
+  for merge_group in merge_groups:
+    v0 = merge_group[0]
+    vM = merge_func(v0, merge_group)
+    if vM:
+      res.append(vM)
+  return res
+
+def GroupStably(all_values, key_func):
+  """Groups an array by key_func, with the groups returned in a stable order.
+
+  Returns a list of groups.
+  """
+  all_values = list(all_values)
+
+  merge_groups = {}
+  merge_groups_in_creation_order = []
+  for value in all_values:
+    key = key_func(value)
+    if key not in merge_groups:
+      merge_groups[key] = []
+      merge_groups_in_creation_order.append(merge_groups[key])
+    merge_groups[key].append(value)
+  return merge_groups_in_creation_order