比如，在id=1的样本中，只要出现了a=1,那么b在任何年份都为1，只有变量a在所有年份都为0，那么b才取值为0。我想生成满足这样条件的变量b,该什么实现呢？<br>
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* Example generated by -dataex-. To install: ssc install dataex
clear
input float(id year a b)
1 2000 0 1
1 2001 1 1
1 2002 0 1
1 2004 1 1
2 2001 0 0
2 2002 0 0
3 2003 1 1
4 2000 1 1
4 2001 1 1
4 2003 0 1
end
复制代码<br>
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