1.关于观察值个数问题。
设定两个变量，一个字符型变量，一个实数型变量，每个棉量下面都有很多数据，可是用gen: n=_n生成的观察值个数为1，这个1到底指什么？

2.在打开一个文件时出现了如下指示:
no room to add more observations
    An attempt was made to increase the number of observations beyond what is currently possible.  You
    have the following alternatives:

     1.  Store your variables more efficiently; see help compress.  (Think of Stata's data area as the
         area of a rectangle; Stata can trade off width and length.)

     2.  Drop some variables or observations; see help drop.

     3.  Increase the amount of memory allocated to the data area using the set memory command; see help
         memory.

之前的都已经clear了，怎么会出现空间不足的情况呢？求该情况最简便的解决办法