我有一个data.frame或tibble,在一个脚本中,写入CSV文件。在另一个脚本中,相同的CSV文件被读入data.frame或tibble。使用read_csv()
,用col_types=
,参数,我可以指定列类型在阅读下面是一个例子:
# Create an example dataframe
df <- tibble::tibble(a=1L
, b=1.0
, c="a"
, d=TRUE
, e=lubridate::ymd_hms("2019-03-19T13:15:18Z")
, f=lubridate::ymd("2019-03-19")
, g=factor("a"))
# Write csv to file
readr::write_csv(df, "temp.csv")
# read it back in, supplying a col_types string spec
readr::read_csv("temp.csv", col_types="idclTDf")
#> # A tibble: 1 x 7
#> a b c d e f g
#> <int> <dbl> <chr> <lgl> <dttm> <date> <fct>
#> 1 1 1 a TRUE 2019-03-19 13:15:18 2019-03-19 a
由reprex包创建于2019-03-19 (v0.2.1)
问题是我需要知道函数的col_types=
参数read_csv()
(或让它猜测,我不想这样做)。我想要的是获取原文的一些方法df
,在我写出来之前,col_types
从df
对象生成字符串,可以用来读取转储的CSV。也就是说,我想要一些能够创建"idclTDf"
字符串的东西data.frame作为参数。
我看到这里有一个功能请求(我已经加了我的两分钱):https://github.com/tidyverse/readr/issues/895。
发布于 2019-03-20 14:27:51
我确实有一个解决方案,它可以工作,但我认为它非常不完整而且没有硬化。这是我尝试解决方案。
# https://github.com/tidyverse/readr/issues/895
# Create function to take a tibble and return a character string that can be used in `readr::read_csv()`
# as the `col_types` argument to re-read this back into a dataframe after it had been written out
# by `write_csv()`.
get_col_types_short <- function(.df) {
# Get column classes from input dataframe
lst_col_classes__ <- purrr::map(.df, ~ class(.x))
# Map classes to known single-character col_types indicator
vl_col_class_char__ <- purrr::map_chr(lst_col_classes__, function(.e) {
dplyr::case_when(
"logical" %in% .e ~ "l"
, "integer" %in% .e ~ "i"
, "numeric" %in% .e ~ "d"
, "double" %in% .e ~ "d"
, "character" %in% .e ~ "c"
, "factor" %in% .e ~ "f"
, "Date" %in% .e ~ "D"
, "POSIXct" %in% .e ~ "T"
, TRUE ~ "c"
)
})
# Return vector of single-character col_type indicator.
# Element name is the source column it came from.
vl_col_class_char__
}
# Test it:
df <- tibble::tibble(a=1L
, b=1.0
, c="a"
, d=TRUE
, e=lubridate::ymd_hms("2019-03-19T13:15:18Z")
, f=lubridate::ymd("2019-03-19")
, g=factor("a"))
v__ <- get_col_types_short(df)
# Show what is actually returned
v__
#> a b c d e f g
#> "i" "d" "c" "l" "T" "D" "f"
# Collapse it to show how to use it
paste(v__, collapse="")
#> [1] "idclTDf"
# Write csv to file
readr::write_csv(df, "temp.csv")
# read it back in, using the above col_types string spec
readr::read_csv("temp.csv", col_types=paste(v__, collapse=""))
#> # A tibble: 1 x 7
#> a b c d e f g
#> <int> <dbl> <chr> <lgl> <dttm> <date> <fct>
#> 1 1 1 a TRUE 2019-03-19 13:15:18 2019-03-19 a
由reprex包创建于2019-03-19 (v0.2.1)
https://stackoverflow.com/questions/-100008979
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