rangestat for (cumulative) rolling standard deviations

[River Huang]

Dear All, The following question comes from http://bbs.pinggu.org/thread-6298239-1-1.html.
The end is to obtain, for each `group_id', the standard deviation of `var1' from the very first observation till the current observation (in the order of `order').

* Example generated by -dataex-. To install: ssc install dataex
clear
input float(group_id var1 var2 order)
1 2 3  1
1 4 2  2
1 4 5  3
1 3 1  4
1 2 2  5
2 2 3  1
2 4 2  2
2 4 5  3
2 3 1  4
2 2 2  5
2 2 3  6
2 4 2  7
2 4 5  8
2 3 1  9
2 2 2 10
end

Any suggestion is highly appreciated.

[Robert Picard]

rangestat (sd) var1, interval(order . 0) by(group_id)

[River Huang]

Dear Robert, Many thanks. As I expected, it should be relatively easy for -rangestat- command to do the task. However, I always have trouble in understanding how to use -interval( )- option in some cases.