What is the most efficient way to cast a list as a data frame?

Question

Very often I want to convert a list wherein each index has identical element types to a data frame. For example, I may have a list:

> my.list
[[1]]
[[1]]         


        

Answer 1

Not sure where they rank as far as efficiency, but depending on the structure of your lists there are some tidyverse options. A bonus is that they work nicely with unequal length lists:

l <- list(a = list(var.1 = 1, var.2 = 2, var.3 = 3)
        , b = list(var.1 = 4, var.2 = 5)
        , c = list(var.1 = 7, var.3 = 9)
        , d = list(var.1 = 10, var.2 = 11, var.3 = NA))

df <- dplyr::bind_rows(l)
df <- purrr::map_df(l, dplyr::bind_rows)
df <- purrr::map_df(l, ~.x)

# all create the same data frame:
# A tibble: 4 x 3
  var.1 var.2 var.3
    
1     1     2     3
2     4     5    NA
3     7    NA     9
4    10    11    NA

And you can also mix vectors and data frames:

library(dplyr)
bind_rows(
  list(a = 1, b = 2),
  data_frame(a = 3:4, b = 5:6),
  c(a = 7)
)

# A tibble: 4 x 2
      a     b
   
1     1     2
2     3     5
3     4     6
4     7    NA