list 添加数据框作为列表元素（使用 for 循环）
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Adding data frames as list elements (using for loop)
提问by Riccardo
I have in my environment a series of data frames called EOG. There is one for each year between 2006 and 2012. Like, EOG2006, EOG2007...EOG2012. I would like to add them as elements of a list.
我的环境中有一系列名为 EOG 的数据框。2006 年到 2012 年之间每年都有一个。例如，EOG2006、EOG2007...EOG2012。我想将它们添加为列表的元素。
First, I am trying to know if this is possible. I read the official R guide and a couple of R programming manuals but I didn't find explicit examples about that.
首先，我想知道这是否可能。我阅读了官方 R 指南和一些 R 编程手册，但我没有找到明确的例子。
Second, I would like to do this using a for loop. Unfortunately, the code I used to do the job is wrong and I am going crazy to fix it.
其次，我想使用 for 循环来做到这一点。不幸的是，我用来做这项工作的代码是错误的，我要疯狂地修复它。
for (j in 2006:2012){
z<-j
sEOG<-paste("EOG", z, sep="")
dEOG<-get(paste("EOG", z, sep=""))
lsEOG<-list()
lsEOG[[sEOG]]<-dEOG
}
This returns a list with one single element. Where is the mistake?
这将返回一个包含一个元素的列表。错误在哪里？
回答by Christopher Louden
You keep reinitializing the list inside the loop. You need to move lsEOG<-list()outside the forloop.
您不断重新初始化循环内的列表。您需要将lsEOG<-list()外for循环。
lsEOG<-list()
for (j in 2006:2012){
z <- j
sEOG <- paste("EOG", z, sep="")
dEOG <- get(paste("EOG", z, sep=""))
lsEOG[[sEOG]] <-dEOG
}
Also, you can use jdirectly in the pastefunctions:
此外，您可以j直接在paste函数中使用：
sEOG <- paste("EOG", j, sep="")
回答by RickC
I had the same question, but felt that the OP's initial code was a bit opaque for R beginners. So, here is perhaps a bit clearer example of how to create data frames in a loop and add them to a list which I just now figured out by playing around in the R shell:
我有同样的问题，但觉得 OP 的初始代码对于 R 初学者来说有点不透明。因此，这里可能是一个更清晰的示例，说明如何在循环中创建数据帧并将它们添加到我刚刚通过在 R shell 中玩弄的列表中：
> dfList <- list() ## create empty list
>
> for ( i in 1:5 ) {
+ x <- rnorm( 4 )
+ y <- sin( x )
+ dfList[[i]] <- data.frame( x, y ) ## create and add new data frame
+ }
>
> length( dfList ) ## 5 data frames in list
[1] 5
>
> dfList[[1]] ## print 1st data frame
x y
1 -0.3782376 -0.3692832
2 -1.3581489 -0.9774756
3 1.2175467 0.9382535
4 -0.7544750 -0.6849062
>
> dfList[[2]] ## print 2nd data frame
x y
1 -0.1211670 -0.1208707
2 -1.5318212 -0.9992406
3 0.8790863 0.7701564
4 1.4014124 0.9856888
>
> dfList[[2]][4,2] ## in 2nd data frame, print element in row 4 column 2
[1] 0.9856888
>
For R beginners like me, note that double brackets are required to access the ith data frame. Basically, double brackets are used for lists while single brackets are used for vectors.
对于像我这样的 R 初学者，请注意访问第 i 个数据框需要双括号。基本上，双括号用于列表，而单括号用于向量。
回答by llrs
If the data frames are saved as an object you can find them by apropos("EOG", ignore.case=FALSE)and them with a loop store them in the list:
如果数据框被保存为一个对象，你可以通过apropos("EOG", ignore.case=FALSE)循环找到它们，并将它们存储在列表中：
list.EOG<- apropos("EOG", ignore.case=FALSE) #Find the objects with case sensitive
lsEOG<-NULL #Creates the object to full fill in the list
for (j in 1:length(list.EOG)){
lsEOG[i]<-get(list.EOG[i]) #Add the data.frame to each element of the list
}
to add the name of each one to the list you can use:
要将每个人的名称添加到您可以使用的列表中：
names(lsEOG, "names")<-list.EOG
