subset() 函数:
subset(dataset , subset , select )
dataset 是要进行操作的数据集
subset 是对数据的某些字段进行操作
select 选取要显示的字段
```{r spdep}
hightech
aa = subset(hightech,year==2001&province=="北京",select = c("year","province","PAT"))
bb = subset(hightech,year==2001|province=="北京",select = c("year","province","NPO"))
aa
bb