r 读入多个 .dat 文件

Question

嗨，我是新来的，也是 R 的初学者，

我的问题:
如果我在 R 中有多个文件(test1.dat，test2.dat，...)可以使用，我使用此代码读取它们

filelist <- list.files(pattern = "*.dat")

df_list <- lapply(filelist, function(x) read.table(x, header = FALSE, sep = ","
                                               ,colClasses = "factor", comment.char = "", 
                                               col.names = "raw"))

现在我遇到了数据很大的问题，我找到了一个使用 sqldf-package 加快速度的解决方案:

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"))

它适用于一个文件，但我无法像第一个代码片段那样更改代码以读入多个文件。有人能帮我吗？谢谢!沫沫

Answer 1

这似乎有效(但我认为有更快的 sql 方法)

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)))

查看速度 - 部分摘自 mnel 的帖子 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))

阅读: 数据表

filelist <- list.files(pattern = "*.dat")

system.time(df_list <- lapply(filelist, fread))

#  user  system elapsed 
# 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))))

#    user  system elapsed 
#  35.594   1.432  37.357 

检查 - 除属性外似乎没问题

all.equal(df_list , df_list2)