提取时接近preserving对象的属性/替换操作 [英] Approaches to preserving object's attributes during extract/replace operations

问题描述

最近我在R $ C $ç遇到了以下问题。在一个函数，接受一个数据帧作为一个参数，我需要根据数据帧的原始列的值与计算出的数据添加（或更换，如果存在的话）的列。我写了code，但测试显示，数据帧的提取/替换操作，我已经使用，导致该对象的特殊（用户自定义）属性的损失

意识到，并通过读取R文件（的 http://stat.ethz.ch/R-manual/R-patched/library/base/html/Extract.html ），我决定非常简单地解决问题 - 通过的节能的提取物之前的属性/替换操作和恢复的他们此后

  myTransformationFunction＆LT;  - 功能（数据）{  ＃保存对象的属性
  ATTRS＆LT;  - 属性（数据）  ＆lt;数据帧的转换;涉及的`data`＆GT提取/替换操作;  ＃恢复属性
  属性（数据）＆LT;  -  ATTRS  返回（数据）
}
 

这方法奏效。然而，一不小心，我遇到另一块R文件的跑了（的http://stat.ethz.ch/R-manual/R-patched/library/base/html/Extract.data.frame.html),它提供恕我直言一个有趣的（和潜在的，更通用的？）的另一种方法以解决同样的问题：

  ##保持特殊属性：使用类与
##as.data.frame和[的方法：as.data.frame.avector＆LT;  -  as.data.frame.vector`[.avector`＆LT;  - 功能（X，I，...）{
  为r  -  NextMethod（[）
  mostattributes（R）LT;  - 属性（X）
   -  [R
}D＆下;  -  data.frame（ⅰ= 0：7中，f = GL（2,4），
                U =结构（11:18，单位=公斤的class =avector））
STR（D [2：4，-1]）＃'U'保持它的单位
 

我真的AP preciate如果这里的人们可以通过帮助：

1. 比较上述的两种方法，如果他们有可比性（我认识到，所定义的第二种方法是为数据帧，但我怀疑它可以推广到任何物体）




2. 解释中函数定义的语法和含义在第二个方法，尤其是 as.data.frame.avector ，如还有什么是行 as.data.frame.avector＆LT的目的; - as.data.frame.vector

解决方案

我回答我的问题，因为我刚刚发现了一个SO问题（<一个href=\"http://stackoverflow.com/questions/10404224/how-to-delete-a-row-from-a-data-frame-without-losing-the-attributes\">How删除从data.frame行不失属性的），答案覆盖上面的最我提出的问题。然而，更多的解释（的R初学者的）的第二种方法仍然是AP preciated。

更新：

另一种解决这个问题已经在答案提出以下的SO问题：索引操作删除属性。就个人而言，不过，我更喜欢这种方法的基础上，创建一个新的类，它的语义恕我直言清洁。

Recently I encountered the following problem in my R code. In a function, accepting a data frame as an argument, I needed to add (or replace, if it exists) a column with data calculated based on values of the data frame's original column. I wrote the code, but the testing revealed that data frame extract/replace operations, which I've used, resulted in a loss of the object's special (user-defined) attributes.

After realizing that and confirming that behavior by reading R documentation (http://stat.ethz.ch/R-manual/R-patched/library/base/html/Extract.html), I decided to solve the problem very simply - by saving the attributes before the extract/replace operations and restoring them thereafter:

myTransformationFunction <- function (data) {

  # save object's attributes
  attrs <- attributes(data)

  <data frame transformations; involves extract/replace operations on `data`>

  # restore the attributes
  attributes(data) <- attrs

  return (data)
}

This approach worked. However, accidentally, I ran across another piece of R documentation (http://stat.ethz.ch/R-manual/R-patched/library/base/html/Extract.data.frame.html), which offers IMHO an interesting (and, potentially, a more generic?) alternative approach to solving the same problem:

## keeping special attributes: use a class with a
## "as.data.frame" and "[" method:

as.data.frame.avector <- as.data.frame.vector

`[.avector` <- function(x,i,...) {
  r <- NextMethod("[")
  mostattributes(r) <- attributes(x)
  r
}

d <- data.frame(i = 0:7, f = gl(2,4),
                u = structure(11:18, unit = "kg", class = "avector"))
str(d[2:4, -1]) # 'u' keeps its "unit"

I would really appreciate if people here could help by:

1. Comparing the two above-mentioned approaches, if they are comparable (I realize that the second approach as defined is for data frames, but I suspect it can be generalized to any object);

2. Explaining the syntax and meaning in the function definition in the second approach, especially as.data.frame.avector, as well as what is the purpose of the line as.data.frame.avector <- as.data.frame.vector.

解决方案

I'm answering my own question, since I have just found an SO question (How to delete a row from a data.frame without losing the attributes), answers to which cover most of my questions posed above. However, additional explanations (for R beginners) for the second approach would still be appreciated.

UPDATE:

Another solution to this problem has been proposed in an answer to the following SO question: indexing operation removes attributes. Personally, however, I better like the approach, based on creating a new class, as it's IMHO semantically cleaner.

这篇关于提取时接近preserving对象的属性/替换操作的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！