【问题】

有时候不仅需要删数据，还需要按相应规则增加数据。

比如：怎么从左图到右图？
http://s9/middle/629bb758t7a558c792308&690113：expand扩展样本" TITLE="Tips 113：expand扩展样本" />

【方法】

expand

expand replaces each observation in the dataset with n copies of the observation, where n is equal to the required expression rounded to the nearest integer.  If the expression is less than 1 or equal to missing, it is interpreted as if it were 1, and the observation is retained but not duplicated.

【例子】

use http://www.stata-press.com/data/r11/expandxmpl

list

expand n

list

*还有其他相关命令：

*expandcl — Duplicate clustered observations