在read.table / read.csv中指定colClasses参数的自定义日期格式 [英] Specify custom Date format for colClasses argument in read.table/read.csv

问题描述

在read.table / read.csv中使用colClasses参数有一种方法来指定Date格式吗？

（我意识到我可以在导入之后进行转换，但是有很多这样的日期列，在导入步骤中会更容易）

(I realise I can convert after importing, but with many date columns like this, it would be easier to do it in the import step)

我有一个.csv，日期列格式为％d /％m /％Y 。

I have a .csv with date columns in the format %d/%m/%Y.

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

这样会导致转换错误。例如， 15/07/2008 成为 0015-07-20 。

This gets the conversion wrong. For example, 15/07/2008 becomes 0015-07-20.

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

这里的输出如下：

推荐答案

您可以编写自己的接受字符串的函数使用您想要的格式将其转换为日期，然后使用 setAs 将其设置为作为方法。然后，您可以使用您的函数作为colClasses的一部分。

You can write your own function that accepts a string and converts it to a Date using the format you want, then use the setAs to set it as an as method. Then you can use your function as part of the colClasses.

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)

然后修改如果需要为您的数据工作。

Then modify if needed to work for your data.

编辑---

你可能要首先运行 setClass（'myDate'）以避免警告（您可以忽略该警告，但是如果您这么做很可能会令人烦恼，这是一个简单的电话，摆脱它）。

You might want to run setClass('myDate') first to avoid the warning (you can ignore the warning, but it can get annoying if you do this a lot and this is a simple call that gets rid of it).

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