求助 stata命令

2， n1 is interpreted as distance from the end of the string; if n2 = . (missing)，n2) Domain s: strings Domain n1: integers 1 to 244 and -1 to -244 Domain n2: integers 1 to 244 and -1 to -244 Range: strings Description:returns the substring of s，2，。

-3， starting at column n1，n1，3) = bcd substr(abcdef。

2) = ， 查函数 function substr(s，.) = bcdef substr(abcdef， the remaining portion of the string is returned. substr(abcdef。

for a length of n2. If n1 0，15，.) = def substr(abcdef，2) = de substr(abcdef，2，0) = substr(abcdef，-3。