cbind（）正在更改日期格式 [英] cbind() is changing date formatting

问题描述

我正在尝试创建数据框的子集，当我这样做时，R会切换日期列的格式。任何想法为什么或如何解决这个问题？

I'm trying to create a subset of a data frame and when I do so, R switches the formatting of the date column. Any idea why or how to fix this?

> head(spyPr2)
        Date   Open   High    Low  Close    Volume Adj.Close
1 12/30/2011 126.02 126.33 125.50 125.50  95599000    125.50
2 12/29/2011 125.24 126.25 124.86 126.12 123507200    126.12
3 12/28/2011 126.51 126.53 124.73 124.83 119107100    124.83
4 12/27/2011 126.17 126.82 126.06 126.49  86075700    126.49
5 12/23/2011 125.67 126.43 125.41 126.39  92187200    126.39
6 12/22/2011 124.63 125.40 124.23 125.27 119465400    125.27
> spyPr2$Date <- as.Date(spyPr2$Date, format = "%m/%d/%Y")
> head(spyPr2)
        Date   Open   High    Low  Close    Volume Adj.Close
1 2011-12-30 126.02 126.33 125.50 125.50  95599000    125.50
2 2011-12-29 125.24 126.25 124.86 126.12 123507200    126.12
3 2011-12-28 126.51 126.53 124.73 124.83 119107100    124.83
4 2011-12-27 126.17 126.82 126.06 126.49  86075700    126.49
5 2011-12-23 125.67 126.43 125.41 126.39  92187200    126.39
6 2011-12-22 124.63 125.40 124.23 125.27 119465400    125.27
> spyPr2 <- data.frame(cbind(spyPr2$Date, spyPr2$Close, spyPr2$Adj.Close))
> str(spyPr2)
'data.frame':   1638 obs. of  3 variables:
 $ X1: num  15338 15337 15336 15335 15331 ...
 $ X2: num  126 126 125 126 126 ...
 $ X3: num  126 126 125 126 126 ...
> head(spyPr2)
     X1     X2     X3
1 15338 125.50 125.50
2 15337 126.12 126.12
3 15336 124.83 124.83
4 15335 126.49 126.49
5 15331 126.39 126.39
6 15330 125.27 125.27

更新：

> spyPr2 <- data.frame(cbind(spyPr2["Date"], spyPr2$Close, spyPr2$Adj.Close))
Error in `[.data.frame`(spyPr2, "Date") : undefined columns selected
> spyPr2 <- data.frame(cbind(spyPr2[,"Date"], spyPr2$Close, spyPr2$Adj.Close))
Error in `[.data.frame`(spyPr2, , "Date") : undefined columns selected

更新2：

structure(list(Date = structure(c(15338, 15337, 15336, 15335, 
15331, 15330), class = "Date"), Open = c(126.02, 125.24, 126.51, 
126.17, 125.67, 124.63), High = c(126.33, 126.25, 126.53, 126.82, 
126.43, 125.4), Low = c(125.5, 124.86, 124.73, 126.06, 125.41, 
124.23), Close = c(125.5, 126.12, 124.83, 126.49, 126.39, 125.27
), Volume = c(95599000L, 123507200L, 119107100L, 86075700L, 92187200L, 
119465400L), Adj.Close = c(125.5, 126.12, 124.83, 126.49, 126.39, 
125.27)), .Names = c("Date", "Open", "High", "Low", "Close", 
"Volume", "Adj.Close"), row.names = c(NA, -6L), class = "data.frame")

推荐答案

明显的答案是不要做这样的子集化！使用适当的工具。

Obvious answer is don't do subsetting like that! Use the appropriate tools. What is wrong with

spyPr2.new <- spyPr2[, c("Date", "Close", "Adj.Close")]

？

解释你看到的行为，你需要了解什么是 $ 返回以及 cbind（）的工作原理。 cbind（）是R中的其中之一，其中方法调度不是通过常规方法完成的，而是通过埋在R内部的特殊代码处理。这就是 cbind（）之后的R代码：

To explain the behaviour you are seeing, you need to understand what $ returns and how cbind() works. cbind() is one of those oddities in R wherein method dispatch is not done via the usual method but is instead handled via special code buried in the internals of R. This is all the R code behind cbind():

> cbind
function (..., deparse.level = 1) 
.Internal(cbind(deparse.level, ...))
<bytecode: 0x24fa0c0>
<environment: namespace:base>

没有多少帮助，呃？有数据框的方法和ts对象：

Not much help, eh? There are methods for data frames and "ts" objects however:

> methods(cbind)
[1] cbind.data.frame cbind.ts*       

   Non-visible functions are asterisked

在我做揭示之前，还要注意什么 $ 返回（ dat2 是将 Date 转换为Date对象）后的6行数据：

Before I do the reveal, also note what $ returns (dat2 is your 6 lines of data after converting Date to a "Date" object):

> str(dat2$Date)
 Date[1:6], format: "2011-12-30" "2011-12-29" "2011-12-28" "2011-12-27" ...

这是一个Date这是一个特殊的矢量。

This is a "Date" object, which is a special vector really.

> class(dat2$Date)
[1] "Date"

关键是它不是数据帧。所以当你使用 cbind（）时，内部代码看到三个向量，内部代码创建一个矩阵。

The key thing is that it is not a data frame. So when you use cbind(), the internal code is seeing three vectors and the internal code creates a matrix.

> (c1 <- cbind(dat2$Date, dat2$Close, dat2$Adj.Close))
      [,1]   [,2]   [,3]
[1,] 15338 125.50 125.50
[2,] 15337 126.12 126.12
[3,] 15336 124.83 124.83
[4,] 15335 126.49 126.49
[5,] 15331 126.39 126.39
[6,] 15330 125.27 125.27
> class(c1)
[1] "matrix"

只能有数字或字符R中的矩阵，所以 Date 对象被转换为数字向量：

There can only be numeric or character matrices in R so the Date object is converted to a numeric vector:

> as.numeric(dat2$Date)
[1] 15338 15337 15336 15335 15331 15330

允许 cbind（）生成数字矩阵。

您可以强制使用数据框架方法直接调用它，它知道如何处理Date对象，因此不进行任何转换：

You can force the use of the data frame method by calling it explicitly and it does know how to handle "Date" objects and so doesn't do any conversion:

> cbind.data.frame(dat2$Date, dat2$Close, dat2$Adj.Close)
   dat2$Date dat2$Close dat2$Adj.Close
1 2011-12-30     125.50         125.50
2 2011-12-29     126.12         126.12
3 2011-12-28     124.83         124.83
4 2011-12-27     126.49         126.49
5 2011-12-23     126.39         126.39
6 2011-12-22     125.27         125.27

然而，除了所有的解释，你正在努力做子集以非常复杂的方式。 [作为子集功能工作正常：

However, all the explanation aside, you are trying to do the subsetting in a very complex manner. [ as a subset function works just fine:

> dat2[, c("Date", "Close", "Adj.Close")]
        Date  Close Adj.Close
1 2011-12-30 125.50    125.50
2 2011-12-29 126.12    126.12
3 2011-12-28 124.83    124.83
4 2011-12-27 126.49    126.49
5 2011-12-23 126.39    126.39
6 2011-12-22 125.27    125.27

subset（）也是一个选项但不需要这里：

subset() is also an option but not needed here:

> subset(dat2, select = c("Date", "Close", "Adj.Close"))
        Date  Close Adj.Close
1 2011-12-30 125.50    125.50
2 2011-12-29 126.12    126.12
3 2011-12-28 124.83    124.83
4 2011-12-27 126.49    126.49
5 2011-12-23 126.39    126.39
6 2011-12-22 125.27    125.27

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