如何在多列上选择一个条件的行？

Question

我需要选择一个数据框的所有行，在其中一列中可以找到值“ x”。

如果列数很小，我可以这样做：

dat1=data.frame(vec1=c("x","a","b","b","b","a","x","b","b","a"),
                vec2=c("a","a","b","a","b","a","a","b","b","a"),
                vec3=c("x","b","b","b","b","a","b","b","b","b"),
                value=c(1,2,42,3,7,30,31,32,4,14))

dat2=dat1[which(dat1$vec1=="x" | dat1$vec2=="x" | dat1$vec3=="x"),]

问题是我有很多列（从vec1到vec40）。有没有一种快速的方法来选择我想要的所有行？

谢谢您的帮助！