Would like to do simple math on aggregations of documents, eg collectd disk plugin has free and used integer values and would like to calculate:

% disk free: free/(used+free)

derivitive of disk usage to predict when a disk will run out of space: -(free)/d(free)/dt

similarly interface plugin in collectd is a total of bytes tx and rx and need to calculate derivative of rx and tx to see bytes/time

This is easy to do in graphite which has many useful functions, eg "most deviant" which pulls out the top 5 metrics based on standard deviation.

would rather have everything in elastic than to split numeric time series into graphite