r - 无法将类 ‘c("fseq", "function")’ 强制转换为 data.frame

Question

这会产生一个 1 列的 data.frame:

library(tidyverse)
library(jsonlite)
library(purrr)

symbols <- 'https://api.exchangerate.host/symbols' %>% fromJSON %>% .$symbols

symbols %>% 
  {
  data.frame(code = map_chr(., ~ .x$code ) %>% unname)
  }
# 1 column data.frame:
#     code
# 1    AED
# 2    AFN
# 3    ALL
# 4    AMD

然而这个错误

symbols %>% 
  {
  data.frame(code = . %>% map_chr(~ .x$code ) %>% unname)
  }
 # Error in as.data.frame.default(x[[i]], optional = TRUE) : 
 #  cannot coerce class ‘c("fseq", "function")’ to a data.frame

为什么管道到 purrr::map_chr()错误，我们怎样才能让它工作？

Answer 1

我没有收到该错误消息，但我收到了 0 行数据框。尝试这个 :

symbols %>% 
{
   data.frame(code = purrr::map_chr(., ~.x$code) %>% unname())
}

也许，这更干净:

symbols %>% map_chr(~.x$code ) %>% unname %>% data.frame(code = .)