在read.table/read.csv中为colClasses参数指定自定义日期格式

Question

题:

有没有办法在read.table/read.csv中使用colClasses参数时指定Date格式？

(我意识到我可以在导入后进行转换,但是有很多像这样的日期列,在导入步骤中更容易实现)

---

例:

我有一个.csv格式的日期列%d/%m/%Y.

dataImport <- read.csv("data.csv", colClasses = c("factor","factor","Date"))

这会导致转换错误.例如,15/07/2008成为0015-07-20.

---

可重现的代码:

data <- 
structure(list(func_loc = structure(c(1L, 2L, 3L, 3L, 3L, 3L, 
3L, 4L, 4L, 5L), .Label = c("3076WAG0003", "3076WAG0004", "3076WAG0007", 
"3076WAG0009", "3076WAG0010"), class = "factor"), order_type = structure(c(3L, 
3L, 1L, 1L, 1L, 1L, 2L, 2L, 3L, 1L), .Label = c("PM01", "PM02", 
"PM03"), class = "factor"), actual_finish = structure(c(4L, 6L, 
1L, 2L, 3L, 7L, 1L, 8L, 1L, 5L), .Label = c("", "11/03/2008", 
"14/08/2008", "15/07/2008", "17/03/2008", "19/01/2009", "22/09/2008", 
"6/09/2007"), class = "factor")), .Names = c("func_loc", "order_type", 
"actual_finish"), row.names = c(NA, 10L), class = "data.frame")


write.csv(data,"data.csv", row.names = F)                                                        

dataImport <- read.csv("data.csv")
str(dataImport)
dataImport

dataImport <- read.csv("data.csv", colClasses = c("factor","factor","Date"))
str(dataImport)
dataImport

这是输出的样子:

Answer 1

您可以编写自己的函数来接受字符串并使用您想要的格式将其转换为Date,然后使用setAs它将其设置为as方法.然后,您可以将您的函数用作colClasses的一部分.

尝试:

setAs("character","myDate", function(from) as.Date(from, format="%d/%m/%Y") )

tmp <- c("1, 15/08/2008", "2, 23/05/2010")
con <- textConnection(tmp)

tmp2 <- read.csv(con, colClasses=c('numeric','myDate'), header=FALSE)
str(tmp2)

然后根据需要进行修改以适用于您的数据.

编辑---

您可能希望先运行setClass('myDate')以避免警告(您可以忽略该警告,但如果您执行此操作会很烦人,这是一个简单的调用,可以摆脱它).

Answer 2

如果您只想更改1种日期格式,则可以使用该Defaults软件包更改其中的默认格式as.Date.character

library(Defaults)
setDefaults('as.Date.character', format = '%d/%M/%Y')
dataImport <- read.csv("data.csv", colClasses = c("factor","factor","Date"))
str(dataImport)
## 'data.frame':    10 obs. of  3 variables:
##  $ func_loc     : Factor w/ 5 levels "3076WAG0003",..: 1 2 3 3 3 3 3 4 4 5
##  $ order_type   : Factor w/ 3 levels "PM01","PM02",..: 3 3 1 1 1 1 2 2 3 1
##  $ actual_finish: Date, format: "2008-10-15" "2009-10-19" NA "2008-10-11" ...

我认为@Greg Snow的答案要好得多,因为它不会改变常用函数的默认行为.

Answer 3

如果您还需要时间:

setClass('yyyymmdd-hhmmss')
setAs("character","yyyymmdd-hhmmss", function(from) as.POSIXct(from, format="%Y%m%d-%H%M%S"))
d <- read.table(colClasses="yyyymmdd-hhmmss", text="20150711-130153")
str(d)
## 'data.frame':    1 obs. of  1 variable:
## $ V1: POSIXct, format: "2015-07-11 13:01:53"