数据结转

shiyiming

请问一下，如果一个变量中的值为空时，就结转同一个变量上一个值，以此类推，应该如何编程？
即 a
1



2
3
4
变为
a
1
1
1
1
2
3
4

shiyiming

[code:3o1kcmqo]data a;
input a;
cards;
1
.
.
.
2
3
3
.
3
.
4
.
.
;
data c;
set a ;
retain b;
if a>. then b=a;
run;

data d;
set a;
n=_n_;
if missing(a) then do;
   do until (not missing(a));
   n=n-1;
set a(keep=a) point=n; *second SET statement;
end;
end;
run;

data e;
   do until(last.a);
      set a;
      by a notsorted;
      if last.a and not missing(a) then do;
      b = a;
      end;  
      if missing(a) then do;
      a=b;
      end;  
      output;
   end;
run;
[/code:3o1kcmqo]
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shiyiming

[code:2tk1jckq]

data a;
input a;
cards;
1
&#46;
&#46;
&#46;
2
3
3
&#46;
3
&#46;
4
&#46;
&#46;
;
data c(drop=b impute);
set a ;
retain b;
if a&gt;&#46; then b=a;
if missing(a) and not missing(b) then do;
        impute=1;
        a=b;
end;
run;


proc print;
run;



[/code:2tk1jckq]

shiyiming

[code:1a8ylxqs]data result(drop=tmp);
        set a(rename=(a=tmp));
        retain a;
        if not missing(tmp) then a=tmp;
run;[/code:1a8ylxqs]