[程式] SAS中LAG程式無法用在if...then

[faceoflove56 (1234567)]

[軟體程式類別]:
SAS

[程式問題]:
目前遇到一個問題
lag函數無法用再if...then語法中
但我想把資料整理成

Name  Nth
---------------------
ID1    0
ID1    1
ID1    2
ID2    0
ID2    1
ID2    2
ID2    3

我原先使用的語法為
data
  set
  if first.name then Nth=0;
  if Name=lag(Name) then Nth=Lag(Nth)+1;
run;

想請問該如何修改，感謝。

[軟體熟悉度]:
低(1~3個月)


[問題敘述]:
Lag函數無法應用於if...then

[程式範例]:
已貼在程式問題
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※ 編輯: faceoflove56 (140.119.120.6), 06/17/2015 11:16:16
推 BugEater: LAG is called in conditional code, the value it
→ BugEater: returened is not the value from the previous
→ BugEater: but is the value of its previous execution.
→ BugEater: try this. data A;set A; by name;
→ BugEater: if first.name then Nth=0;
→ BugEater: Nth=Lag(Nth)+1;run;
→ faceoflove56: 感謝>"<
→ luenchang: It's not recommended to use LAG() within a logical
→ luenchang: condition (i.e. if then). Check out how the LAG()
→ luenchang: works in this article
→ luenchang: "Please Don't Lag Behind LAG! "