没有名称的rbind data.frames [英] rbind data.frames without names

问题描述

我试图找出当加入没有名称的data.frames时，为什么 rbind 功能不能正常工作。
这是我的测试：

I am trying to figure out why the rbind function is not working as intended when joining data.frames without names. Here is my testing:

test <- data.frame(
            id=rep(c("a","b"),each=3),
            time=rep(1:3,2),
            black=1:6,
            white=1:6,
            stringsAsFactors=FALSE
            )

# take some subsets with different names
pt1 <- test[,c(1,2,3)]
pt2 <- test[,c(1,2,4)]

# method 1 - rename to same names - works
names(pt2) <- names(pt1)
rbind(pt1,pt2)

# method 2 - works - even with duplicate names
names(pt1) <- letters[c(1,1,1)]
names(pt2) <- letters[c(1,1,1)]
rbind(pt1,pt2)

# method 3 - works  - with a vector of NA's as names
names(pt1) <- rep(NA,ncol(pt1))
names(pt2) <- rep(NA,ncol(pt2))
rbind(pt1,pt2)

# method 4 - but... does not work without names at all?
pt1 <- unname(pt1)
pt2 <- unname(pt2)
rbind(pt1,pt2)

这对我来说似乎有点奇怪。我错过了一个很好的理由，为什么这不应该开箱即用？

This seems a bit odd to me. Am I missing a good reason why this shouldn't work out of the box?

修改附加信息

使用@ JoshO'Brien的建议 debug ，我可以将错误发现在此中，如果声明部分 rbind.data.frame 函数

Using @JoshO'Brien's suggestion to debug, I can identify the error as occurring during this if statement part of the rbind.data.frame function

if (is.null(pi) || is.na(jj <- pi[[j]]))

（在线代码这里： http://svn.r-project.org/R/trunk/src/library/base/R/dataframe.R 起始于： ###这里是rbind和cbind的方法

(online version of code here: http://svn.r-project.org/R/trunk/src/library/base/R/dataframe.R starting at: "### Here are the methods for rbind and cbind.")

从程序开始， pi 的值似乎没有在这一点上被设置，因此程序试图索引内置的常量 pi 像 pi [[3]] 和错误出来。

From stepping through the program, the value of pi does not appear to have been set at this point, hence the program tries to index the built-in constant pi like pi[[3]] and errors out.

从我可以看出，内部的 pi 对象似乎没有设置，因为这个较早的行，其中 clabs 已初始化为 NULL ：

From what I can figure, the internal pi object doesn't appear to be set due to this earlier line where clabs has been initialized as NULL:

if (is.null(clabs)) clabs <- names(xi) else { #pi gets set here

我正在纠结一下试图弄清楚这一点，但会更新为一起来。

I am in a tangle trying to figure this out, but will update as it comes together.

推荐答案

因为 unname（）显式地将NA分配为列标题不是相同的动作。当列名称全部为NA时，则可以使用 rbind（）。由于 rbind（）取数据框的名称/列名，结果与&因此 rbind（）失败。

Because unname() & explicitly assigning NA as column headers are not identical actions. When the column names are all NA, then an rbind() is possible. Since rbind() takes the names/colnames of the data frame, the results do not match & hence rbind() fails.

这是一些代码，以帮助看到我的意思：

Here is some code to help see what I mean:

> c1 <- c(1,2,3)
> c2 <- c('A','B','C')
> df1 <- data.frame(c1,c2)
> df1
  c1 c2
1  1  A
2  2  B
3  3  C
> df2 <- data.frame(c1,c2) # df1 & df2 are identical
>
> #Let's perform unname on one data frame &
> #replacement with NA on the other
>
> unname(df1)
  NA NA
1  1  A
2  2  B
3  3  C
> tem1 <- names(unname(df1))
> tem1
NULL
>
> #Please note above that the column headers though showing as NA are null
>
> names(df2) <- rep(NA,ncol(df2))
> df2
  NA NA
1  1  A
2  2  B
3  3  C
> tem2 <- names(df2)
> tem2
[1] NA NA
> 
> #Though unname(df1) & df2 look identical, they aren't
> #Also note difference in tem1 & tem2
>
> identical(unname(df1),df2)
[1] FALSE
> 

我希望这有帮助。名称显示为每个NA，但两个操作是不同的。
因此，将其列标题替换为NA的2个数据帧可以是rbound，但是没有任何列标题的2个数据帧（使用 unname（）实现）不能。

I hope this helps. The names show up as NA each, but the two operations are different. Hence, 2 data frames with their column headers replaced to NA can be "rbound" but 2 data frames without any column headers (achieved using unname()) cannot.

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