Update dateframes to add the function elapse_time.

modules/plugin_event/__init__.py

@@ -10,6 +10,7 @@ from dataframes import (active_period,
                         DATE_MIN,
                         db2df,
                         debug_df,
+                        elapse_time,
                         expand_per_year,
                         full_name,
                         get_column_names,

modules/plugin_event/dataframes.py

@@ -193,6 +193,27 @@ def debug_df(df, opt=""):
         print df
 
 
+def elapse_time(start_date, end_date, xdate):
+    """Vectorized function to compute the elapse time between the starting date
+    and xdate or end_date:
+
+        * it is computed between the start_date and the end_date
+          when the end_date is above xdate
+        * otherwise it is computed between the start_date and xdate
+
+    Args:
+        start_date (pandas.Series): starting date for items
+        end_date (pandas.Series): ending date for items
+        xdate (date)
+
+    Returns:
+        pandas.Series:
+            with the timedelta in days
+
+    """
+    return end_date.mask(end_date > xdate, xdate) - start_date
+
+
 def expand_per_year(df, year_start, year_end):
     """Expand the list of active items between year_start and year_end to
     a list of active items per year. An item appears several time when it