在R中将长格式组数据重组为宽格式

我不认为这只是一种从长到宽的格式，但我的数据现在是这样的：

dat <- data.frame(group = c(rep(1, 4), rep(2, 3)),
           member = c(seq(1, 4), seq(1, 3)),
           name = letters[1:7],
           id = seq(1:7))

dat
dat2 <- data.frame(group = c(rep(1, 4), rep(2, 3)),
                  name = letters[1:7],
                  id = seq(1:7),
                  member1 = c("b", "a", "a", "a", "f", "e", "e"),
                  member2 = c("c", "c", "b", "b", "g", "g", "f"),
                  member3 = c("d", "d", "d", "c", NA, NA, NA))