在深度使用Map来cbind中的列

Question

I am trying to cbind a column to a list within a list, without success. If list was of depth 1, the example would look as follows, where I would like to add dates to my example data frames in each list object:

ex_df_plain <- list(cbind(1,2), 
                cbind(3,4))
Map(cbind, as.list(c(2016, 2017)), ex_df_plain)

[[1]]
     [,1] [,2] [,3]
[1,] 2016    1    2

[[2]]
     [,1] [,2] [,3]
[1,] 2017    3    4

But as soon as I try to apply this to a list object where the depth of the list is greater than 1, the cbind reduces the list elements instead of combining:

at_depth_df <- list(as.list(c(1,2)), as.list(c(3,4)))

Map(cbind, 
    list(as.list(c(2015, 2016)), as.list(c(2017, 2018))),
    at_depth_df)

[[1]]
     [,1] [,2]
[1,] 2015 1   
[2,] 2016 2   

[[2]]
     [,1] [,2]
[1,] 2017 3   
[2,] 2018 4

My expected output should be

[[1]]
[[1]][[1]]
     [,1] [,2]
[1,] 2015    1

[[1]][[2]]
     [,1] [,2]
[1,] 2016    2


[[2]]
[[2]][[1]]
     [,1] [,2]
[1,] 2017    3

[[2]][[2]]
     [,1] [,2]
[1,] 2018    4

Answer 1

We need a recursive Map

Map(function(x, y) Map(cbind, x, y), lst1, at_depth_df)

where

lst1 <- list(as.list(c(2015, 2016)), as.list(c(2017, 2018)))

---

We can write a function to do this

f1 <- function(x, y, fun) {
    if(is.atomic(x)  && is.atomic(y)) {
      x1 <- match.fun(fun)(x,y)
      dimnames(x1) <- NULL
      x1
       } else {
         Map(f1, x, y, MoreArgs = list(fun = fun))
    }
}

f1(lst1, at_depth_df, cbind)
#[[1]]
#[[1]][[1]]
#     [,1] [,2]
#[1,] 2015    1

#[[1]][[2]]
#     [,1] [,2]
#[1,] 2016    2


#[[2]]
#[[2]][[1]]
#     [,1] [,2]
#[1,] 2017    3

#[[2]][[2]]
#     [,1] [,2]
#[1,] 2018    4