读入多个.dat文件 [英] r read in multiple .dat-files
问题描述
你好我是新来的,在R里面是初学者,
我的问题:
在我有多个文件的情况下(test1.dat, test2.dat,...)在R中使用我使用这段代码在
filelist< - list .files(pattern =* .dat)
df_list< - lapply(filelist,function(x)read.table(x,header = FALSE,sep =,
,colClasses =factor,comment.char =,
col.names =raw))
现在我遇到了问题,我的数据很大,我找到了一个解决方案来加速使用sqldf-package:
sql< - file(test2.dat)
df< - sqldf(select * from sql,dbname = tempfile(),
file.format = list header = FALSE,row.names = FALSE,colClasses =factor,
comment.char =,col.names =raw))
这对于一个文件来说工作的很好,但是我不能像第一个代码片段那样改变代码来读入多个文件。有人能帮我吗?谢谢! Momo
这似乎工作(但我假设有一个更快的 sql
sql.l< - lapply(filelist,file)
df_list2 < - lapply(sql.l,function(i)sqldf(select * from i),
dbname = tempfile(),file.format = list(header = TRUE,row.names = FALSE)) )
速度 - 部分来自mnel的帖子快速阅读在R中使用大表作为数据框
library(data.table)
library(sqldf)
测试数据
n = 1e6
DT = data.table(a = sample(1:1000,n,replace = TRUE),
b = sample(1:1000 ,n,replace = TRUE),
c = rnorm(n),
d = sample(c(foo,bar,baz,qux,quux), replace = TRUE),
e = rnorm(n),
f = sample(1:1000,n,replace = TRUE))
#写出5个文件
lapply(1:5,function i)write.table(DT,paste0(test,i,.dat),
sep =,,row.names = FALSE,quote = FALSE))
阅读: data.table
<$ p $文件列表filelist < - list.files(pattern =* .dat)
system.time(df_list< - lapply(filelist,fread))
#user system已过期
#5.244 0.200 5.457
阅读: sqldf
sql.l< - lapply(filelist,file)
system.time(df_list2< - lapply(sql.l,function(i)sqldf(select * from i),
dbname = tempfile(),file.format = list(header = TRUE,row.names = FALSE))))
#已用用户系统
#35.594 1.432 37.357
检查 - 除了属性外似乎没问题
all。相等(df_list,df_list2)
Hi I am new here and a beginner in R,
My problem: in the case i have more than one file (test1.dat, test2.dat,...) to work with in R i use this code to read them in
filelist <- list.files(pattern = "*.dat")
df_list <- lapply(filelist, function(x) read.table(x, header = FALSE, sep = ","
,colClasses = "factor", comment.char = "",
col.names = "raw"))
Now i have the problem that my data is big, i found a solution to speed things up using the sqldf-package :
sql <- file("test2.dat")
df <- sqldf("select * from sql", dbname = tempfile(),
file.format = list(header = FALSE, row.names = FALSE, colClasses = "factor",
comment.char = "", col.names ="raw"))
it is working well for one file but i am not able to change the code to read-in multiple files like in the first code snippet. can someone help me? Thank you! Momo
This seems to work (but i assume there is a quicker sql
way to this)
sql.l <- lapply(filelist , file)
df_list2 <- lapply(sql.l, function(i) sqldf("select * from i" ,
dbname = tempfile(), file.format = list(header = TRUE, row.names = FALSE)))
Look at speeds - partially taken from mnel's post Quickly reading very large tables as dataframes in R
library(data.table)
library(sqldf)
# test data
n=1e6
DT = data.table( a=sample(1:1000,n,replace=TRUE),
b=sample(1:1000,n,replace=TRUE),
c=rnorm(n),
d=sample(c("foo","bar","baz","qux","quux"),n,replace=TRUE),
e=rnorm(n),
f=sample(1:1000,n,replace=TRUE) )
# write 5 files out
lapply(1:5, function(i) write.table(DT,paste0("test", i, ".dat"),
sep=",",row.names=FALSE,quote=FALSE))
read: data.table
filelist <- list.files(pattern = "*.dat")
system.time(df_list <- lapply(filelist, fread))
# user system elapsed
# 5.244 0.200 5.457
read: sqldf
sql.l <- lapply(filelist , file)
system.time(df_list2 <- lapply(sql.l, function(i) sqldf("select * from i" ,
dbname = tempfile(), file.format = list(header = TRUE, row.names = FALSE))))
# user system elapsed
# 35.594 1.432 37.357
Check - seems ok except for attributes
all.equal(df_list , df_list2)
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