add generator which yields drawn randomly from a histogram interpreted as a pdf.

1 files changed, 9 insertions, 0 deletions

diff --git a/generator/vertex.py b/generator/vertex.py
index 5626541..450c0e4 100644
--- a/generator/vertex.py
+++ b/generator/vertex.py
@@ -4,9 +4,18 @@ from itertools import izip, count
 from chroma.pi0 import pi0_decay
 from chroma.event import Event, Subtrack
 from chroma.sample import uniform_sphere
+from chroma.itertoolset import repeat_func
 
 # generator parts for use with gun()
 
+def from_histogram(h):
+    "Yield values drawn randomly from the histogram `h` interpreted as a pdf."
+    pdf = h.hist/h.hist.sum()
+    cdf = np.cumsum(pdf)
+
+    for x in repeat_func(np.random.random_sample):
+        yield h.bincenters[np.searchsorted(cdf, x)]
+
 def constant(obj):
     while True:
         yield obj