4月 032010
 


Definition: Special missing value is a type of numeric missing value that enables you to represent different categories of missing data by using the letters A-Z or an underscore. Ref: SAS 9.1.3 language reference: concepts page no: 102 The symbol usually used to represent a missing value for a numerical variable is the period or dot. Aside from the dot, there are 27 special missing values SAS can store in numerical variables. They are the dot-underscore (._), and dot-letter (.A thru .Z). Note that these special values are case insensitive. That is, .A=.a .B=.b .C=.c etc. If you do not begin a special numeric missing value with a period, SAS identifies it as a variable name. Therefore, to use a special numeric missing value in a SAS expression or assignment statement, you must begin the value with a period, followed by the letter or underscore, as in the following example: x=.d; When SAS prints a special missing value, it prints only the letter. When data values contain characters...

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