将列表类型转换为R，data.frame和as.data.frame中的数据帧类型不起作用

Question

I have created A with command data.frame in R, but the data type of A is "list", and I have already tried to convert A to data frame with as.data.frame but it does work, anyone else has same experience? the code are below:

A <- data.frame(rep(1,5), row.names=c("A","B","C","D","E"), check.rows = FALSE, check.names = FALSE)
mode(A)
A1 <- as.data.frame(A)
mode(A1)

Answer 1

As data.frame is a list with length of each list element ( column ) same, the mode returns a list . We can use

class(A)
#[1] "data.frame"

and

is.data.frame(A)
#[1] TRUE

from @RHertel's commments

is.list(A)  
#[1] TRUE

or

str(A)
#'data.frame':   5 obs. of  1 variable:
# $ rep(1, 5): num  1 1 1 1 1

dput(A)

to confirm that a data.frame is also a list .

But, list also can have equal length and not a data.frame

l1 <- as.list(1:5)
mode(l1)
#[1] "list"
class(l1)
#[1] "list"