将几个数据帧合并到一个带有循环的数据帧中 [英] Merge several data.frames into one data.frame with a loop
问题描述
我试图将 merge
几个 data.frames
放入一个 data.frame
。由于我有一个完整的文件列表,我试图用循环结构来完成。
到目前为止,循环方法工作正常。然而,它看起来效率很低,我想知道是否有一个更快,更容易的方法。
这是情景:
我有一个目录有几个 .csv
文件。每个文件都包含可用作合并变量的相同标识符。由于文件的大小相当大,我以为一次只读一个文件到R中,而不是一次读取所有文件。
因此,我用 list.files
获取目录的所有文件,并读入前两个文件。之后我用 merge
来得到一个 data.frame
。
FileNames< - list.files(path =... / tempDataFolder /)
FirstFile< - read.csv(file = paste(... / tempDataFolder /,FileNames [1],sep =),
header = T,na.strings =NULL)
SecondFile < - read.csv(file = paste( ../tempDataFolder/,FileNames [2],sep =),
header = T,na.strings =NULL)
dataMerge< - merge(FirstFile,SecondFile,by = c(COUNTRYNAME,COUNTRYCODE,Year),
all = T)
<现在我用一个作为
循环来获取所有剩余的 .csv
文件和 merge
它们到已经存在的 data.frame
中:
<$ c (文件名)){
ReadInMerge< - read.csv(file = paste(... / tempDataFolder /,FileNames [i],sep =) ,
header = T,na.strings =NULL)
dataMerge< - merge(dataMerge,ReadInMerge,by = c(COUNTRY NAME,COUNTRYCODE,Year),
all = T)
}
即使它工作的很好,我想知道是否有一个更优雅的方式来完成这项工作吗? 解决方案
你可能想看看在相关的问题在stackoverflow 。
我会分两步来处理这个问题:导入所有数据(使用 plyr
),然后合并到一起:
文件名< - list.files(path =... / tempDataFolder /,full.names = TRUE)
library(plyr)
import.list< - llply(filenames,read.csv)
这将给你一个你现在需要合并在一起的所有文件的列表。有很多方法可以做到这一点,但这里有一个方法(使用 Reduce
):
<$ (x,y)合并(x,y,all = T,
by = c(COUNTRYNAME,COUNTRYCODE,Year)),导入。 list,accumulate = F)
或者,您可以使用重塑如果您对
包: Reduce
不满意,
library(reshape)
data< - merge_recurse(import.list)
I am trying to merge
several data.frames
into one data.frame
. Since I have a whole list of files I am trying to do it with a loop structure.
So far the loop approach works fine. However, it looks pretty inefficient and I am wondering if there is a faster and easier approach.
Here is the scenario:
I have a directory with several .csv
files. Each file contains the same identifier which can be used as the merger variable. Since the files are rather large in size I thought to read each file one at a time into R instead of reading all files at once.
So I get all the files of the directory with list.files
and read in the first two files. Afterwards I use merge
to get one data.frame
.
FileNames <- list.files(path=".../tempDataFolder/")
FirstFile <- read.csv(file=paste(".../tempDataFolder/", FileNames[1], sep=""),
header=T, na.strings="NULL")
SecondFile <- read.csv(file=paste(".../tempDataFolder/", FileNames[2], sep=""),
header=T, na.strings="NULL")
dataMerge <- merge(FirstFile, SecondFile, by=c("COUNTRYNAME", "COUNTRYCODE", "Year"),
all=T)
Now I use a for
loop to get all the remaining .csv
files and merge
them into the already existing data.frame
:
for(i in 3:length(FileNames)){
ReadInMerge <- read.csv(file=paste(".../tempDataFolder/", FileNames[i], sep=""),
header=T, na.strings="NULL")
dataMerge <- merge(dataMerge, ReadInMerge, by=c("COUNTRYNAME", "COUNTRYCODE", "Year"),
all=T)
}
Even though it works just fine I was wondering if there is a more elegant way to get the job done?
You may want to look at the closely related question on stackoverflow.
I would approach this in two steps: import all the data (with plyr
), then merge it together:
filenames <- list.files(path=".../tempDataFolder/", full.names=TRUE)
library(plyr)
import.list <- llply(filenames, read.csv)
That will give you a list of all the files that you now need to merge together. There are many ways to do this, but here's one approach (with Reduce
):
data <- Reduce(function(x, y) merge(x, y, all=T,
by=c("COUNTRYNAME", "COUNTRYCODE", "Year")), import.list, accumulate=F)
Alternatively, you can do this with the reshape
package if you aren't comfortable with Reduce
:
library(reshape)
data <- merge_recurse(import.list)
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