使用 rbind 时，r 数据帧和矩阵会产生不同的行名称

Question

方法一：

df1<-data.frame(A=1:5,B=2:6)
df2<-data.frame(A=1:5,B=2:6)
df3<-rbind(df1,df2)
row.names(df3)
 [1] "1"  "2"  "3"  "4"  "5"  "6"  "7"  "8"  "9"  "10"

方法二：

df1<-data.frame(matrix(data = c(1:5,2:6),
                       nrow = 5,
                       dimnames = list(c(1:5),c("A","B"))))
df2<-data.frame(matrix(data = c(1:5,2:6),
                       nrow = 5,
                       dimnames = list(c(1:5),c("A","B"))))
df3<-rbind(df1,df2)
row.names(df3)
 [1] "1"  "2"  "3"  "4"  "5"  "11" "21" "31" "41" "51"

我知道行名应该是唯一的值，我想知道为什么Mehtod1和方法2在行名中生成不同的结果？

Answer 1

在方法1中，行名是整数

df1 <- data.frame(A=1:5,B=2:6)
df2 <- data.frame(A=1:5,B=2:6)

dput(df1)
structure(list(A = 1:5, B = 2:6), class = "data.frame", row.names = c(NA,
-5L))

并且在

rbind

之后它们保持整数

df3 <- rbind(df1,df2)

dput(df3)
structure(list(A = c(1L, 2L, 3L, 4L, 5L, 1L, 2L, 3L, 4L, 5L),
    B = c(2L, 3L, 4L, 5L, 6L, 2L, 3L, 4L, 5L, 6L)), row.names = c(NA,
-10L), class = "data.frame")

在方法2中，行名是字符串

df1 <- data.frame(matrix(data = c(1:5,2:6),
                         nrow = 5,
                         dimnames = list(c(1:5),c("A","B"))))
df2 <- data.frame(matrix(data = c(1:5,2:6),
                         nrow = 5,
                         dimnames = list(c(1:5),c("A","B"))))

dput(df1)
structure(list(A = 1:5, B = 2:6), class = "data.frame", row.names = c("1",
"2", "3", "4", "5"))

并且在

rbind

之后它们也仍然保留原来的类，字符串

dput(df3)
structure(list(A = c(1L, 2L, 3L, 4L, 5L, 1L, 2L, 3L, 4L, 5L),
    B = c(2L, 3L, 4L, 5L, 6L, 2L, 3L, 4L, 5L, 6L)), row.names = c("1",
"2", "3", "4", "5", "11", "21", "31", "41", "51"), class = "data.frame")

字符串无法枚举，因此通过向字符串添加索引来使其唯一。