enhance/add histogram sample (#137)

visualdl/server/lib.py

@@ -146,7 +146,7 @@ def get_histogram_tags(storage):
  return get_tags(storage, 'histogram')
 
 
-def get_histogram(storage, mode, tag):
+def get_histogram(storage, mode, tag, num_samples=200):
  with storage.mode(mode) as reader:
  histogram = reader.histogram(tag)
  res = []
@@ -171,7 +171,22 @@ def get_histogram(storage, mode, tag):
  [instance.left(),
  instance.right(),
  instance.frequency()])
- return res
+ if len(res) < num_samples:
+ return res
+
+ # sample some steps
+ span = float(len(res)) / (num_samples - 1)
+ span_offset = 0
+ data_idx = 0
+
+ sampled_data = []
+ data_size = len(res)
+ while data_idx < data_size:
+ sampled_data.append(res[data_size - data_idx - 1])
+ span_offset += 1
+ data_idx = int(span_offset * span)
+ sampled_data.append(res[0])
+ return sampled_data[::-1]
 
 
 def retry(ntimes, function, time2sleep, *args, **kwargs):