3.10 批量读取 csv 文件

iris 数据转化为 data.table 类型，按照 Species 分组拆成单独的 csv 文件，各个文件的文件名用鸢尾花的类别名表示

# 批量分组导出
library(data.table)
as.data.table(iris)[, fwrite(.SD, paste0("data/user_", unique(Species), ".csv")), by = Species, .SDcols = colnames(iris)]

读取文件夹 data/ 所有 csv 数据文件

library(data.table)
merged_df <- do.call('rbind', lapply(list.files(pattern = "*.csv", path = "data/"), fread ) )
# 或者
merged_df <- rbindlist(lapply(list.files(pattern = "*.csv", path = "data/"), fread ))

xdf$date <- as.Date(xdf$date)
xdf$ts <- as.POSIXct(as.numeric(xdf$ts), origin = "1978-01-01")
split(xdf[order(xdf$ts), ], interaction(xdf$study, xdf$port)) %>%
  lapply(function(.x) {
    .x[nrow(.x), ]
  }) %>%
  unname() %>%
  Filter(function(.x) {
    nrow(.x) > 0
  }, .) %>%
  do.call(rbind.data.frame, .)

library(dplyr)
xdf %>%
  mutate(
    date = as.Date(date),
    ts = anytime::anytime(as.numeric(ts))
  ) %>%
  arrange(ts) %>%
  group_by(study, port) %>%
  slice(n()) %>%
  ungroup()

library(tibble)
mtcars <- tibble(mtcars)
print(mtcars, n = 6, width = 69)

## # A tibble: 32 × 11
##     mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb
##   <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
## 1  21       6   160   110  3.9   2.62  16.5     0     1     4     4
## 2  21       6   160   110  3.9   2.88  17.0     0     1     4     4
## 3  22.8     4   108    93  3.85  2.32  18.6     1     1     4     1
## 4  21.4     6   258   110  3.08  3.22  19.4     1     0     3     1
## 5  18.7     8   360   175  3.15  3.44  17.0     0     0     3     2
## 6  18.1     6   225   105  2.76  3.46  20.2     1     0     3     1
## # ℹ 26 more rows