R語言觀察日誌(part5)--利用readr和readxl包讀寫數據

學習筆記，僅供參考

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利用readr和readxl包讀寫數據

讀取數據

• 相關函數

函數包readr和readxl提供了一系列的數據讀入功能，主要函數如下：

#readr包

read_delim(file, delim, quote = "\"", escape_backslash = FALSE,
            escape_double = TRUE, col_names = TRUE, col_types = NULL,
            locale = default_locale(), na = c("", "NA"), quoted_na = TRUE,
            comment = "", trim_ws = FALSE, skip = 0, n_max = Inf,
            guess_max = min(1000, n_max), progress = show_progress(),
            skip_empty_rows = TRUE)

read_csv(file, col_names = TRUE, col_types = NULL,
        locale = default_locale(), na = c("", "NA"), quoted_na = TRUE,
        quote = "\"", comment = "", trim_ws = TRUE, skip = 0,
        n_max = Inf, guess_max = min(1000, n_max),
        progress = show_progress(), skip_empty_rows = TRUE)
 
#readxl包
read_excel(path, sheet = NULL, range = NULL, col_names = TRUE,
  		  col_types = NULL, na = "", trim_ws = TRUE, skip = 0,
  		  n_max = Inf, guess_max = min(1000, n_max),
  		  progress = readxl_progress(), .name_repair = "unique")

read_xls(path, sheet = NULL, range = NULL, col_names = TRUE,
	col_types = NULL, na = "", trim_ws = TRUE, skip = 0,
	n_max = Inf, guess_max = min(1000, n_max),
	progress = readxl_progress(), .name_repair = "unique")

• 參數

• 舉個例子

輸入：

library(readr)
library(readxl)

cp <-read_delim("comp.csv", ",")
cp.csv <- read_csv("comp.csv")
cp.xl <- read_excel("comp.xlsx")
#summary(cp.csv)
#summary(cp.xl)

system.time(read_csv("data.csv"))
system.time(read.csv("data.csv"))

輸出：

> system.time(read_csv("data.csv"))
用戶 系統 流逝 
0.88 0.00 0.89 
Warning message:
Duplicated column names deduplicated: 'DATE_R' => 'DATE_R_1' [48] 
> system.time(read.csv("data.csv"))
用戶 系統 流逝 
3.77 0.05 3.86 

通過與R中的read.csv()函數進行比對，我們發現，利用函數包readr和readxl中的函數進行數據讀入的速度有很大提升。

寫入數據

函數包readr提供了數據讀取功能的同時，還提供了數據寫入功能，即將data.frame對象重新寫爲csv, xlsx,等格式的文件。

• 相關函數

write_delim(x, path, delim = " ", na = "NA", append = FALSE,
  col_names = !append, quote_escape = "double")

write_csv(x, path, na = "NA", append = FALSE, col_names = !append,
  quote_escape = "double")

write_excel_csv(x, path, na = "NA", append = FALSE,
  col_names = !append, delim = ",", quote_escape = "double")

• 參數

• 舉個例子

輸入：

df <- data.frame(x = c(1,2,3,4,5), y = c(6,7,NA,9,0))
write_delim(df, "df1.csv", delim = ",")
write_csv(df, "df2.csv", na = "-")

df1.csv：

df2.csv：