replace..if...操作时候stata为什么也会对空值进行赋值

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比如我想将变量abc大于100的值，都替换为100，其中500,600之间是有2个数值是缺失的

abc
1
2
3
4
500
600
120
10
11
12
13
14
15

在输入命令：replace abc = 100 if abc >= 100 后，结果发现“空值”也被赋值为100，不想对空值进行任何操作，该怎么处理呢？
运行结果：

. replace abc = 100 if abc >= 100
(5 real changes made)


abc
1
2
3
4
100
100
100
100
100
10
11
12
13
14
15

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关键词：replace Stata place tata PLA replace

看帮助解释缺失值

Title

    [U] 12.2.1 Missing values

Description
    Stata has 27 numeric missing values:
        ., the default, which is called the "system missing value" or sysmiss
    and
        .a, .b, .c, ..., .z, which are called the "extended missing values".

    Numeric missing values are represented by large positive values.  The
    ordering is

                 all nonmissing numbers < . < .a < .b < ... < .z

    Thus, the expression age > 60 is true if variable age is greater than 60 or missing.

    To exclude missing values, ask whether the value is less than ".".  For instance,

        . list if age > 60 & age < .

    To specify missing values, ask whether the value is greater than or equal to
    ".".  For instance,
        . list if age >=.
    Stata has one string missing value, which is denoted by "" (blank).

replace abc = 100 if abc >= 100  & abc~=.

蓝色 发表于 2016-8-4 17:28
replace abc = 100 if abc >= 100  & abc~=.

非常感谢