子集data.frame按日期 [英] Subset data.frame by date

问题描述

我有一个名为 EPL2011_12 的数据集。我想通过按日期设置原始数据集来创建新的数据集。日期在名为 Date 的列中。日期采用DD-MM-YY格式。

I have a dataset called EPL2011_12. I would like to make new a dataset by subsetting the original by date. The dates are in the column named Date The dates are in DD-MM-YY format.

我尝试过

EPL2011_12FirstHalf <- subset(EPL2011_12, Date > 13-01-12)

和

EPL2011_12FirstHalf <- subset(EPL2011_12, Date > "13-01-12")

，但每次都会收到此错误消息。

but get this error message each time.

Warning message:
In Ops.factor(Date, 13- 1 - 12) : > not meaningful for factors

来说没有意义，我想这意味着R在对待文本而不是数字，为什么它不起作用？

I guess that means R is treating like text instead of a number and that why it won't work?

推荐答案

好吧，它显然不是数字，因为它带有破折号它。错误消息和两个注释告诉您这是一个因素，但注释程序显然正在等待并让消息沉没。Dirk建议您执行以下操作：

Well, it's clearly not a number since it has dashes in it. The error message and the two comments tell you that it is a factor but the commentators are apparently waiting and letting the message sink in. Dirk is suggesting that you do this:

 EPL2011_12$Date2 <- as.Date( as.character(EPL2011_12$Date), "%d-%m-%y")

之后，您可以执行以下操作：

After that you can do this:

 EPL2011_12FirstHalf <- subset(EPL2011_12, Date2 > as.Date("2012-01-13") )

R日期函数假定格式为 YYYY-MM-DD或 YYYY / MM / DD。您确实需要比较类似的类：日期到日期或字符到字符。

R date functions assume the format is either "YYYY-MM-DD" or "YYYY/MM/DD". You do need to compare like classes: date to date, or character to character.

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