rep(c(\"ABC\" ,\"ACD\"), c (123,100)), 希望能帮到你

A=data.frame(ID=c("ABC","ACD","DEF")
             Count=c(123, 100, 50) )

X=rep(A\$ID[1], A\$Count[1] )

X

结果为:
X
  [1] ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC
[17] ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC
[33] ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC
[49] ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC
[65] ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC
[81] ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC
[97] ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC
[113] ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC ABC

或者
A=data.frame(ID=c("ABC","ACD","DEF"),
             Count=c(123, 100, 50) )
attach(A)
n=sum(Count)
Y=rep("A", n)
n.row=nrow(A)
k=1
for(i in 1:(n.row) ){
  Y[k:(k+Count-1) ]=rep(as.character(ID)), Count )
  k=k+Count
}
  
Y

结果为:
[1] "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC"
[12] "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC"
[23] "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC"
[34] "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC"
[45] "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC"
[56] "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC"
[67] "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC"
[78] "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC"
[89] "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC"
[100] "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC"
[111] "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC" "ABC"
[122] "ABC" "ABC" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD"
[133] "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD"
[144] "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD"
[155] "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD"
[166] "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD"
[177] "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD"
[188] "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD"
[199] "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD"
[210] "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD" "ACD"
[221] "ACD" "ACD" "ACD" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF"
[232] "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF"
[243] "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF"
[254] "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF"
[265] "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF" "DEF"

rep(df[,1], df[,2])

非常感谢 cheetahfly ， 方法简单明了。