cumulative-frequency

SQL query for cumulative frequency of list of datetimes

I have a list of times in a database column (representing visits to a website). I need to group them in intervals and then get a 'cumulative frequency' table of those dates. For instance I might have: 9:01 9:04 9:11 9:13 9:22 9:24 9:28 and i want to convert that into 9:05 - 2 9:15 - 4 9:25 - 6 9:30 - 7 How can I do that? Can i ev...

Plot with fewer markers than data points (or a better way to plot CDFs?) [matplotlib, or general plotting help]

I am plotting Cumulative Distribution Functions, with a large number of data points. I am plotting a few lines on the same plot, which are identified with markers as it will be printed in black and white. What I would like are markers evenly spaced in the x-dimension. What I am getting is one marker per data point (and given the number o...