SAS中的FIRST.variable和LAST.variable

最新推荐文章于 2022-02-25 09:50:27 发布

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在SAS中，当处理BY组时，系统会自动设置FIRST.variable和LAST.variable变量来标识每个组的开始和结束。如果某观察值是BY组的第一个，SAS将相应的FIRST.variable设为1；若为最后一个，则LAST.variable设为1。对于数据集中的最后一个观察值，所有LAST.variable变量均设为1。

How SAS Determines FIRST.variable andLAST.variable

When an observation is the first in a BY group, SAS sets the value of FIRST.variable to1 for the variable whose value changed, as well as for all of thevariables that follow in the BY statement. For all other observationsin the BY group, the value of FIRST.variable is 0. Likewise, if the observation is the last in a BY group, SAS setsthe value of LAST.variable to 1 for the variable whose value changes on the next observation, as well as for all of the variables that follow in the BY statement.For all other observations in the BY group, the value of LAST.variable is0. For the last observation in a data set, the value of all LAST.variable variablesare set to 1.