如何将向量分组到向量列表中? [英] How to group a vector into a list of vectors?

问题描述

我有一些看起来像这样的数据(例如，假数据):

I have some data which looks like this (fake data for example's sake):

dressId        color 
6              yellow 
9              red
10             green 
10             purple 
10             yellow 
12             purple 
12             red 

其中颜色是因子向量.不能保证因子的所有可能水平实际上都出现在数据中(例如，蓝色"颜色也可以是水平之一).

where color is a factor vector. It is not guaranteed that all possible levels of the factor actually appear in the data (e.g. the color "blue" could also be one of the levels).

我需要一个向量列表，用于将每件衣服的可用颜色分组:

I need a list of vectors which groups the available colors of each dress:

[[1]]
yellow  

[[2]] 
red    

[[3]] 
green purple yellow 

[[4]] 
purple red 

保留礼服的ID会很好(例如，一个数据框，其中此列表为第二列，ID为第一列)，但这不是必需的.

Preserving the IDs of the dresses would be nice (e.g. a dataframe where this list is the second column and the IDs are the first), but not necessary.

我写了一个循环，遍历数据帧的每一行，当下一个ID相同时，它将颜色添加到向量中. (我确定数据按ID排序).当第一列中的ID更改时，它会将矢量添加到列表中:

I wrote a loop which goes through the dataframe row for row, and while the next ID is the same, it adds the color to a vector. (I am sure that the data is sorted by ID). When the ID in the first column changes, it adds the vector to a list:

result <- NULL 
while(blah blah) 
{
    some code which creates the vector called "colors" 
    result[[dressCounter]] <- colors 
    dressCounter <- dressCounter + 1
}

在努力使所有必要的计数变量正确无误后，我感到沮丧的是，它不起作用.第一次colors是

After wrestling with getting all the necessary counting variables correct, I found out to my dismay that it doesn't work. The first time, colors is

[1] yellow
Levels: green yellow purple red blue

并将其强制为整数，因此result变为2.

and it gets coerced into an integer, so result becomes 2.

在第二个循环重复中，colors仅包含红色，并且result成为简单的整数矢量[1] 2 4.

In the second loop repetition, colors only contains red, and result becomes a simple integer vector, [1] 2 4.

在第三次重复中，colors现在是向量

In the third repetition, colors is a vector now,

[1] green  purple yellow
Levels: green yellow purple red blue 

我得到

result[[3]] <- colors

结果错误[[3]]<-颜色:
提供的元素多于要替换的元素

Error in result[[3]] <- colors :
more elements supplied than there are to replace

我做错了什么?有没有一种初始化result的方法，这样它就不会转换成数值向量，而是变成向量列表?

What am I doing wrong? Is there a way to initialize result so it doesn't get converted into a numeric vector, but becomes a list of vectors?

此外，除了自己动手"之外，还有另一种方法来完成整个工作吗?

Also, is there another way to do the whole thing than "roll my own"?

推荐答案

split.data.frame是组织此问题的好方法；然后提取颜色分量.

split.data.frame is a good way to organize this; then extract the color component.

d <- data.frame(dressId=c(6,9,10,10,10,12,12),
               color=factor(c("yellow","red","green",
                              "purple","yellow",
                              "purple","red"),
                 levels=c("red","orange","yellow",
                          "green","blue","purple")))

我认为您想要的版本实际上是这样的:

I think the version you want is actually this:

ss <- split.data.frame(d,d$dressId)

通过提取颜色分量，您可以得到更像您要求的列表的东西:

You can get something more like the list you requested by extracting the color component:

lapply(ss,"[[","color")

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