先两个数据集读入R，再用B中学号去A中匹配，并提取。

使用什么命令，能具体说明一下吗？

merge by

see here: http://stackoverflow.com/questions/1299871/how-to-join-data-frames-in-r-inner-outer-left-right

Outer join: merge(x = df1, y = df2, by = "CustomerId", all = TRUE)

Left outer: merge(x = df1, y = df2, by = "CustomerId", all.x=TRUE)

Right outer: merge(x = df1, y = df2, by = "CustomerId", all.y=TRUE)

Cross join: merge(x = df1, y = df2, by = NULL)

对的，就是这个东西，正则表达式，又学习了一招，万分感谢