r - R Data.Table 将许多列折叠成 1

Question

DATA = data.frame(x1=c("dog","cat","fox","mouse",NA,NA),
x2=c("dog","cat","rhino", NA, "cat","fox"),
x3=c("dog","cat",NA,NA,"cat","fox"),
WANT=c("dog","cat","fox","mouse","cat","fox"))

我有 x1、x2、x3 的“DATA”，我希望将 x1、x2、x3 折叠成“WANT”，它只使用从 x1 开始的第一个报告值，使用 data.table

标签： rdata.table