Add inital cut of iter_utils with a coupel of iters I needed. Tweak

math_utils population.

2 files changed, 125 insertions, 0 deletions

diff --git a/iter_utils.py b/iter_utils.py
new file mode 100644
index 0000000..897493d
--- /dev/null
+++ b/iter_utils.py
@@ -0,0 +1,119 @@
+#!/usr/bin/env python3
+
+import random
+from collections.abc import Iterator
+from typing import Any, List, Optional
+
+
+class PeekingIterator(Iterator):
+    """An iterator that lets you peek at the next item on deck.
+
+    >>> p = PeekingIterator(iter(range(3)))
+    >>> p.__next__()
+    0
+    >>> p.peek()
+    1
+    >>> p.peek()
+    1
+    >>> p.__next__()
+    1
+    >>> p.__next__()
+    2
+    >>> p.peek() == None
+    True
+    >>> p.__next__()
+    Traceback (most recent call last):
+      ...
+    StopIteration
+    """
+
+    def __init__(self, source_iter: Iterator):
+        self.source_iter = source_iter
+        self.on_deck: List[Any] = []
+
+    def __iter__(self) -> Iterator:
+        return self
+
+    def __next__(self) -> Any:
+        if len(self.on_deck) > 0:
+            return self.on_deck.pop()
+        else:
+            item = self.source_iter.__next__()
+            return item
+
+    def peek(self) -> Optional[Any]:
+        if len(self.on_deck) > 0:
+            return self.on_deck[0]
+        try:
+            item = self.source_iter.__next__()
+            self.on_deck.append(item)
+            return self.peek()
+        except StopIteration:
+            return None
+
+
+class SamplingIterator(Iterator):
+    """An iterator that simply echoes what source_iter produces but also
+    collects a random sample (of size sample_size) of the stream that can
+    be queried via get_random_sample() at any time.
+
+    >>> import collections
+    >>> import random
+
+    >>> random.seed(22)
+    >>> s = SamplingIterator(iter(range(100)), 10)
+    >>> s.__next__()
+    0
+
+    >>> s.__next__()
+    1
+
+    >>> s.resovoir
+    [0, 1]
+
+    >>> collections.deque(s)
+    deque([2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99])
+
+    >>> s()
+    [78, 18, 47, 83, 93, 26, 25, 73, 94, 38]
+
+    """
+
+    def __init__(self, source_iter: Iterator, sample_size: int):
+        self.source_iter = source_iter
+        self.sample_size = sample_size
+        self.resovoir: List[Any] = []
+        self.stream_length_so_far = 0
+
+    def __iter__(self) -> Iterator:
+        return self
+
+    def __next__(self) -> Any:
+        item = self.source_iter.__next__()  # or raise
+        self.stream_length_so_far += 1
+
+        # Filling the resovoir
+        pop = len(self.resovoir)
+        if pop < self.sample_size:
+            self.resovoir.append(item)
+            if self.sample_size == (pop + 1):  # just finished filling...
+                random.shuffle(self.resovoir)
+
+        # Swap this item for one in the resovoir with probabilty
+        # sample_size / stream_length_so_far.  See:
+        #
+        # https://en.wikipedia.org/wiki/Reservoir_sampling
+        else:
+            r = random.randint(0, self.stream_length_so_far)
+            if r < self.sample_size:
+                self.resovoir[r] = item
+        return item
+
+    def __call__(self) -> List[Any]:
+        return self.resovoir
+
+
+if __name__ == '__main__':
+    import doctest
+
+    doctest.testmod()
diff --git a/math_utils.py b/math_utils.py
index 64cd9fb..ed9c2f4 100644
--- a/math_utils.py
+++ b/math_utils.py
@@ -41,6 +41,8 @@ class NumericPopulation(object):
         self.lowers, self.highers = [], []
         self.aggregate = 0.0
         self.sorted_copy: Optional[List[float]] = None
+        self.maximum = None
+        self.minimum = None
 
     def add_number(self, number: float):
         """Adds a number to the population.  Runtime complexity of this
@@ -52,6 +54,10 @@ class NumericPopulation(object):
             heappush(self.lowers, -number)  # for lowers we need a max heap
         self.aggregate += number
         self._rebalance()
+        if not self.maximum or number > self.maximum:
+            self.maximum = number
+        if not self.minimum or number < self.minimum:
+            self.minimum = number
 
     def _rebalance(self):
         if len(self.lowers) - len(self.highers) > 1: