Append a data frame to a list

Question

I\'m trying to figure out how to add a data.frame or data.table to the first position in a list.

Ideally, I want a list structured as follows:

List of 4
         


        

Answer 1

The issue you are having is that to put a data frame anywhere into a list as a single list element, it must be wrapped with list(). Let's have a look.

df <- data.frame(1, 2, 3)
x <- as.list(1:3)

If we just wrap with c(), which is what append() is doing under the hood, we get

c(df)
# $X1
# [1] 1
#
# $X2
# [1] 2
#
# $X3
# [1] 3

But if we wrap it in list() we get the desired list element containing the data frame.

list(df)
# [[1]]
#   X1 X2 X3
# 1  1  2  3

Therefore, since x is already a list, we will need to use the following construct.

c(list(df), x) ## or append(x, list(df), 0)
# [[1]]
#   X1 X2 X3
# 1  1  2  3
#
# [[2]]
# [1] 1
#
# [[3]]
# [1] 2
#
# [[4]]
# [1] 3