为数据框的每个列(变量)创建单独的向量 [英] Create separate vectors for each of a data frame's columns (variables)

问题描述

目标:获取一个数据框，并为其每个列(变量)创建单独的向量.

Goal: Take a data frame and create separate vectors for each of its columns (variables).

以下代码使我接近:

batting <- read.csv("mlb_2014.csv", header = TRUE, sep = ",")
hr <- batting[(batting$HR >= 20 & batting$PA >= 100), ]
var_names <- colnames(hr)
for(i in var_names) {
path <- paste("hr$", i, sep = "")
assign(i, as.vector(path))
}

它将为数据框中的每一列创建一个向量，如下所示:

It creates the a vector for each column in the data frame as shown by the output below:

> ls()
 [1] "AB"          "Age"         "BA"          "batting"     "BB"          "CS"         
 [7] "G"           "GDP"         "H"           "HBP"         "hr"          "HR"         
 [13] "i"           "IBB"         "Lg"          "Name"        "OBP"         "OPS"        
 [19] "OPS."        "PA"          "path"        "Pos.Summary" "R"           "RBI"        
 [25] "SB"          "SF"          "SH"          "SLG"         "SO"          "TB"         
 [31] "Tm"          "var_names"   "X2B"         "X3B"        

到目前为止，一切都很好，直到您调用了其中一个向量.例如:

So far so good until you call one of the vectors. For example:

AB
[1] "hr$AB"

A，所有创建的都是一个元素的字符向量.当我想要创建它时...

Alas, all that is created is a one element character vector. When what I want it to create is this...

> AB <- as.vector(hr$AB)
> AB
[1] 459 456 506 417 492 496 404 430 497 346 494 501 415 370 500 331 501 539 456 443 316 437
[23] 449 526 349 486 432 480 295 489 354 506 315 471

...针对原始数据帧中的每个变量.

...for each variable in the original data frame.

如何让R将字符向量"path"中的元素识别为要在assign函数中调用的对象，而不是将单个字符元素分配给要创建的向量?我想将其保留在循环框架中，因为该项目的主要动机是教会我自己如何使用循环.

How do I get R to recognize the elements in the character vector "path" as objects to call in the assign function, rather than an individual character element to assign to the vector I'm creating? I would like to keep this within the loop frame work, since the main motivation behind this project is teach my self how to use loops.

谢谢！

推荐答案

为此，我们有 list2env :

list2env(iris, .GlobalEnv)
head(Species)
#[1] setosa setosa setosa setosa setosa setosa
#Levels: setosa versicolor virginica

但是，几乎从来没有理由那样污染您的工作空间.

However, there is almost never a reason to pollute your workspace like that.

以下是您可以通过循环执行此操作的方法:

Here is how you can do this with a loop:

var_names <- colnames(iris)
for(i in var_names) {
  assign(i, iris[[i]])
}

请注意，我使用 [[]来访问data.frame列，而不是创建您的 path .如果您将列名用作字符向量，则可以使用(或 [])使用此字符来访问列.

Note that instead of creating your paths I use [[ to access the data.frame columns. If you have a column name as a character vector, that (or [) is the way to use this character to access the column.

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