/// <summary>Try to remove extraneous items from the set of sampled items.</summary>
/// <remarks>
/// Try to remove extraneous items from the set of sampled items. This checks
/// if an item is unnecessary based on the desired error bounds, and merges it
/// with the adjacent item if it is.
/// </remarks>
private void Compress()
{
if (samples.Count < 2)
{
return;
}
ListIterator <SampleQuantiles.SampleItem> it = samples.ListIterator();
SampleQuantiles.SampleItem prev = null;
SampleQuantiles.SampleItem next = it.Next();
while (it.HasNext())
{
prev = next;
next = it.Next();
if (prev.g + next.g + next.delta <= AllowableError(it.PreviousIndex()))
{
next.g += prev.g;
// Remove prev. it.remove() kills the last thing returned.
it.Previous();
it.Previous();
it.Remove();
// it.next() is now equal to next, skip it back forward again
it.Next();
}
}
}
/// <summary>Merges items from buffer into the samples array in one pass.</summary>
/// <remarks>
/// Merges items from buffer into the samples array in one pass.
/// This is more efficient than doing an insert on every item.
/// </remarks>
private void InsertBatch()
{
if (bufferCount == 0)
{
return;
}
Arrays.Sort(buffer, 0, bufferCount);
// Base case: no samples
int start = 0;
if (samples.Count == 0)
{
SampleQuantiles.SampleItem newItem = new SampleQuantiles.SampleItem(buffer[0], 1,
0);
samples.AddItem(newItem);
start++;
}
ListIterator <SampleQuantiles.SampleItem> it = samples.ListIterator();
SampleQuantiles.SampleItem item = it.Next();
for (int i = start; i < bufferCount; i++)
{
long v = buffer[i];
while (it.NextIndex() < samples.Count && item.value < v)
{
item = it.Next();
}
// If we found that bigger item, back up so we insert ourselves before it
if (item.value > v)
{
it.Previous();
}
// We use different indexes for the edge comparisons, because of the above
// if statement that adjusts the iterator
int delta;
if (it.PreviousIndex() == 0 || it.NextIndex() == samples.Count)
{
delta = 0;
}
else
{
delta = ((int)Math.Floor(AllowableError(it.NextIndex()))) - 1;
}
SampleQuantiles.SampleItem newItem = new SampleQuantiles.SampleItem(v, 1, delta);
it.Add(newItem);
item = newItem;
}
bufferCount = 0;
}
/// <summary>Get the estimated value at the specified quantile.</summary>
/// <param name="quantile">Queried quantile, e.g. 0.50 or 0.99.</param>
/// <returns>Estimated value at that quantile.</returns>
private long Query(double quantile)
{
Preconditions.CheckState(!samples.IsEmpty(), "no data in estimator");
int rankMin = 0;
int desired = (int)(quantile * count);
ListIterator <SampleQuantiles.SampleItem> it = samples.ListIterator();
SampleQuantiles.SampleItem prev = null;
SampleQuantiles.SampleItem cur = it.Next();
for (int i = 1; i < samples.Count; i++)
{
prev = cur;
cur = it.Next();
rankMin += prev.g;
if (rankMin + cur.g + cur.delta > desired + (AllowableError(i) / 2))
{
return(prev.value);
}
}
// edge case of wanting max value
return(samples[samples.Count - 1].value);
}