如何聚合R数据帧中的字符值

Question

我有一个数据框，例如

df1 <- data.frame(
         A = c("USA","USA","UK","UK","France"),
         B = c("Boston","New York","Cambridge","Oxford","Paris")
)

我想最终得到一个新的数据框：

df2 <- data.frame(
         A = c("USA","UK","France"),
         B = c("Boston; New York","Cambridge; Oxford","Paris")
)

如何使用paste()作为＆＃34;汇总＆＃34;来汇总A？功能，还是等同于此的东西？提前感谢您提供的任何帮助。

Answer 1

我会使用data.table：

library(data.table)
##
R> (df2 <- data.table(df1)[
  ,.(B = paste0(B, collapse = "; ")),
  by = "A"])
#        A                 B
#1:    USA  Boston; New York
#2:     UK Cambridge; Oxford
#3: France             Paris

如果您坚持要求data.frame获得结果，请在之后使用setDF(df2)。