fread in R导入一个大的.csv文件作为一行的数据框 [英] fread in R imports a large .csv file as a data frame with one row

问题描述

我要导入一个大的.csv文件到R（约50万行），所以我一直在尝试使用fread（）从data.table包作为一个更快的替代read.table（）和read .csv（）。但是，fread（）返回一个数据帧，其中包含一行内的所有数据，即使它具有正确的列数。我发现了一个2013年的错误报告，显示这与整数64数据类相关：

I'm importing a large .csv file into R (about 0.5 million rows), so I've been trying to use fread() from the data.table package as a faster alternative to read.table() and read.csv(). However, fread() returns a data frame with all of the data from the rows inside one row, even though it has the correct number of columns. I found a bug report from 2013 showing this is related to the integer64 data class:

http://r-forge.r-project.org/tracker/index.php?func = detail& aid = 2786& group_id = 240& atid = 975

有任何修复或解决方法吗？

Are there any fixes or ways to get around this?

我想读取的.csv文件是0到10000之间的整数，没有丢失的数据。我在Windows 7计算机上使用R版本2.15.2，版本1.8.8的data.table包。

The .csv file I'm trying to read is entirely integers ranging from 0 - 10000, with no missing data. I'm using R version 2.15.2 on a Windows 7 computer, with version 1.8.8 of the data.table package.

我运行的代码是：

require(data.table)
fread("pre2012_alldatapoints.csv", sep = ",", header= TRUE)-> pre
head(pre)

1: 1 22 -105 22 -105
2: 2 22 -105 22 -105
3: 3 20 -105 20 -105
4: 4 21 -105 21 -105
5: 5 21 -105 21 -105
6: 6 21 -105 21 -105

dim(pre)
[1] 12299  5 #dim returns the correct number of dimensions
#this is a subset of the file I want to import that I've confirmed imports correctly with read.csv

pre[,1]
[1] 1 #but trying to print a column returns this

length(pre[,1])
[1] 1 #and length for any column returns a row length of 1

非常感谢您的帮助！

推荐答案

fread 创建一个 data.table 。 data.table 包附带了一些小插曲。

fread creates a data.table. The data.table package comes with a number of vignettes.

您的精确问题在FAQ 1.1中从 data.table常见问题 - 第一个常见问题解答

Your precise issues is addressed in FAQ 1.1 from the data.table FAQ - the very first FAQ!

默认情况下，第二个参数为 .data.table 是在data.table范围内求值的表达式

By default the second argurment to [.data.table is an expression evaluated within the scope of the data.table

因此 pre [，1] 在 pre 范围内计算 1 。 1 仍然是 1 。如果你想通过列号引用，请使用 with = FALSE pre [，1，with = FALSE]

therefore pre[,1] evaluates 1 within the scope of pre. 1 is still 1. If you want' to reference by column number, use with=FALSE pre[,1,with=FALSE]

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