Use the 'size' function instead of the builtin 'len'.

toarstats/stats_utils.py

@@ -274,7 +274,7 @@ def kth_highest(ser, ref, mtype, k, data_capture):
         :return: The kth highest value
         """
         res = x.sort_values().tail(k)
-        res = res[-k] if len(res) > (k-1) else np.nan
+        res = res[-k] if res.size > (k-1) else np.nan
         return res
 
     res = ser.dropna().resample(RSTAGS[mtype]).apply(hk)