Read a directory of CSV files in R
A consistent tidyverse solution would use readr::read_csv I guess.

You don't need map2 if you don't use .y, map is enough.

You can use read.csv as your .f argument, and leave the rest to the ... in your map call, might be a matter of taste but I prefer it that way as with the formula notation you have to read through to make sure read.csv is the only function called.

as.is doesn't seem necessary if you give column classes already. 

Your mutate call is not necessary, tibble will evaluate lazily the definition of filename given at the previous step.

It seems you really want a "one liner" but in my opinion it would be much clearer in a few steps, I propose the following:

files &lt;- list.files(
  "./",
  full.names = TRUE,
  pattern = "^(accounts|symbols)_201[7-9][0-9]{4}\\.csv$")

data_lst &lt;- map(
  files, 
  read_csv,
  header = FALSE,
  sep = "=",
  coltypes = "ic",
  col_names = c("count", "names"))

tibble(
  file_name = files,
  date = str_extract(filename, "201[7-9][0-9]{4}"),
  type = str_extract(filename, "(accounts|symbols)"),
  data = data_lst)


In fact as you're working with a lot of data files I'd tend to write a for loop instead of a map call, so I could more easily debug and proceed without restarting all if an issue arises.