Method 1:
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"
Method 2:
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"
I understand that the rownames should be unique values, I would like to known why Mehtod1 and Method 2 generate different resutls in the rownames?
In Method 1, the rownames are integers
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))
and they stay integers after rbind
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")
In Method 2, the rownames are strings
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"))
and they also remain the original class, strings, after rbind
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("1",
"2", "3", "4", "5", "11", "21", "31", "41", "51"), class = "data.frame")
Strings can't be enumerated so they are made unique by adding an index to the string.
You can equalize the two by adding row.names=NULL when creating the dataframe from a matrix.
df1 <- data.frame(matrix(data = c(1:5,2:6),
nrow = 5,
dimnames = list(c(1:5),c("A","B"))), row.names=NULL)
dput(df1)
structure(list(A = 1:5, B = 2:6), class = "data.frame", row.names = c(NA,
-5L))