Added a new benchmark for iterating columns

bench/column-iter.py

@@ -0,0 +1,60 @@
+from __future__ import print_function
+import contextlib, time
+import bcolz, numpy
+
+@contextlib.contextmanager
+def ctime(label=""):
+    "Counts the time spent in some context"
+    t = time.time()
+    yield
+    print(label, round(time.time() - t, 3), "sec")
+
+
+N = 1000 * 1000
+
+ct = bcolz.fromiter(((i, i*i, i*i*i) for i in xrange(N)), dtype='i8,i8,i8', count=N)
+
+b = numpy.array(numpy.arange(N) % 2, dtype="bool")
+c = bcolz.carray(b)
+
+sorted_index = range(1, N, 2)
+with ctime():
+    r0 = (ct['f0'][sorted_index]).tolist()
+
+with ctime():
+    r1 = [x.f0 for x in ct.where(b)]
+assert r0 == r1
+
+with ctime():
+    r2 = [x.f0 for x in ct.where(c)]
+assert r0 == r2
+
+with ctime():
+    r3 = [x for x in ct['f0'].where(b)]
+assert r0 == r3
+
+with ctime():
+    r4 = [x for x in ct['f0'].where(c)]
+assert r0 == r4
+
+# sum
+with ctime("sum list"):
+    r5 = sum([x for x in ct['f0'].where(c)])
+
+with ctime("sum generator"):
+    r6 = sum(x for x in ct['f0'].where(c))
+assert r5 == r6
+
+with ctime("sum method"):
+    r7 = bcolz.fromiter((x for x in ct['f0'].where(c)),
+                        dtype=ct['f0'].dtype,
+                        count=c.wheretrue().sum()).sum()
+assert r7 == r5
+
+# sum with no NA's
+with ctime("sum with no NA (list)"):
+    r8 = sum([x for x in ct['f0'].where(c) if x == x])  # x==x check to leave out NA values
+
+# sum with no NA's
+with ctime("sum with no NA (generator)"):
+    r9 = sum((x for x in ct['f0'].where(c) if x == x))  # x==x check to leave out NA values