SAS 嵌套 If 语句产生不正确的结果

Question

身份证号码6 returns 'Underweight' 当它应该 return 'Overweight'。有问题的代码行，即第 30-53 行，包含嵌套的 if 语句并产生一个不希望的结果。这些行的目的是将样本划分为class权重class：体重不足、平均或体重过重。

TITLE 'A SHORT SAS PROGRAM';
OPTIONS LS=72;
* Create data file with height and weight data;

DATA HTWT;
    INPUT ID GENDER $ HEIGHT WEIGHT;
    DATALINES;
1 M 68.5 155.0
2 F 61.2 99.00
3 F 63.0 115.0
4 M 70.0 205.0
5 M 68.6 170.0
6 F 65.1 125.0
7 M 72.4 220.0
;
    * Create a new categorical variable for height;

DATA HTWT;
    SET work.HTWT;

    IF HEIGHT < 68 THEN
        STATURE='Short';

    IF HEIGHT >=68 THEN
        STATURE='Tall';
RUN;

* Create a new categorical variable for weight;

DATA HTWT;
    SET work.HTWT;

    IF GENDER='M' THEN
        IF WEIGHT > 170 THEN
            WEIGHT_CLASS='Overweight';

        IF 170 >=WEIGHT >=150 THEN
            WEIGHT_CLASS='Average';

        IF WEIGHT < 140 THEN
            WEIGHT_CLASS='Underweight';

        ELSE IF GENDER='F' THEN
            IF WEIGHT > 120 THEN
                WEIGHT_CLASS='Overweight';

            IF 120 >=WEIGHT >=100 THEN
                WEIGHT_CLASS='Average';

            IF WEIGHT < 100 THEN
                WEIGHT_CLASS='Underweight';
        RUN;

        * Changing units of height from inches to centimeters;

        DATA HTWT;
            SET work.HTWT;
            HEIGHT=2.54 * HEIGHT;
        RUN;

        * Creates HEALTH_INDEX;

        DATA HTWT;
            SET work.HTWT;
            HEALTH_INDEX=WEIGHT/HEIGHT;
        RUN;

        * Print the data file HTWT;

        PROC PRINT DATA=HTWT;
            TITLE 'HEIGHT AND WEIGHT DATA';
        RUN;

        * Sorts the data by gender. Some procedures require sorted data;

        PROC SORT DATA=HTWT OUT=sorted;
            BY GENDER;
        RUN;

        * Print the sorted data file;

        PROC PRINT DATA=sorted;
            TITLE 'GENDER SORTED HTWT DATA';
        RUN;

Answer 1

将嵌套的 if 语句修改为：

 IF  GENDER='M' THEN do;
     IF WEIGHT > 170 THEN
        WEIGHT_CLASS='Overweight';

    else if 150 <= Weight <= 170 THEN
        WEIGHT_CLASS='Average';

    else
        WEIGHT_CLASS='Underweight';
    end;

 else do;
    IF WEIGHT > 120 THEN
        WEIGHT_CLASS='Overweight';

    else iF 100 <= Weight =< 120 THEN
        WEIGHT_CLASS='Average';

    else
        WEIGHT_CLASS='Underweight';
 end;

看看有没有效果？

Answer 2

连续的IF语句按顺序处理。因此，由于最后一个正在测试 WEIGHT 是否 < 100，那么当然 6 号被列为体重不足。如果你想控制执行顺序，添加一些 ELSE and/or DO/END 块。您的基本结构可能应该如下所示。

if A then do;
  if B then xxx ;
  else if C then xxx ;
  else if D then xxxx ;
end;

Answer 3

请不要接受我的答案是正确的，因为我来晚了，而之前的答案清晰有用。但我在这里给你一个简单的建议，当你必须连接很多嵌套的 if 语句时，请使用 select when 语句（来自 sql 语言）给所有可能的层变量的值。

data want;
set have;
if gender='M' then do;
select (weight);
   when (>x) weight_class='';
   when (<y) weight_class='';
   otherwise weight_class=''
end;
end;
else if gender='F' then do;
select (weight);
   when (>x) weight_class='';
   when (<y) weight_class='';
   otherwise weight_class=''
end;
end;
run;

Answer 4

If 语句很有用，但有时创建格式并使用 put 语句进行赋值会更安全。如果您必须执行大量 IF，则尤其如此，因为至少在我的情况下，我输入的内容越多，我搞砸的机会就越大。

使用 put 语句的代码更容易检查和维护。

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