尝试浏览R4DS第20章的列表列部分时出现错误
# Required Libraries
library(tidyverse)
library(modelr)
library(gapminder)
# Created nested data frame
# Each row is a group (one country through time)
by_country <- gapminder %>%
group_by(country,continent) %>%
nest()
# lm function for life expectancy and years
country_model <- function(df) {
lm(lifeExp ~ year, data = df)
}
# Save the lm results back into the data frame
by_country <- by_country %>%
mutate(model = map(.$data, country_model))
eval（predvars，data，env）中的错误：找不到对象'lifeExp'
> sessionInfo()
R version 3.5.0 (2018-04-23)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)
Matrix products: default
locale:
[1] LC_COLLATE=English_United States.1252 LC_CTYPE=English_United
States.1252 LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C LC_TIME=English_United States.1252
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] gapminder_0.3.0 modelr_0.1.4 forcats_0.3.0 stringr_1.4.0 dplyr_0.8.0.1 purrr_0.3.0 readr_1.3.1
[8] tidyr_0.8.2 tibble_2.1.1 ggplot2_3.1.0 tidyverse_1.2.1
loaded via a namespace (and not attached):
[1] Rcpp_1.0.1 cellranger_1.1.0 pillar_1.3.1 compiler_3.5.0 plyr_1.8.4 tools_3.5.0 jsonlite_1.6
[8] lubridate_1.7.4 gtable_0.2.0 nlme_3.1-137 lattice_0.20-38 pkgconfig_2.0.2 rlang_0.3.4 cli_1.1.0
[15] rstudioapi_0.9.0 yaml_2.2.0 haven_2.0.0 withr_2.1.2 xml2_1.2.0 httr_1.4.0 generics_0.0.2
[22] hms_0.4.2 grid_3.5.0 tidyselect_0.2.5 glue_1.3.1 R6_2.4.0 readxl_1.2.0 magrittr_1.5
[29] backports_1.1.3 scales_1.0.0 rvest_0.3.2 assertthat_0.2.1 colorspace_1.4-0 stringi_1.4.3 lazyeval_0.2.2
[36] munsell_0.5.0 broom_0.5.1 crayon_1.3.4