如何使用/dev/stdin和read.csv()从终端读取输入? [英] How to read input from the terminal using /dev/stdin and read.csv()?

问题描述

我正在使用:

R version 3.0.0 (2013-04-03) -- "Masked Marvel"
Platform: x86_64-pc-linux-gnu (64-bit)

我尝试使用read.csv直接从终端输入一些CSV数据段+标头.

I try to use read.csv to input a little CSV data snippet + header, directly from the terminal.

我遇到的问题可能与 R跳过/dev的行有关/stdin 和 read.csv，第一行的标题，第二行的跳过但又足够不同(答案没有解释我在这里看到的内容)，因此可以提出一个单独的问题.

I'm encountering a problem that may be related to R skips lines from /dev/stdin and read.csv, header on first line, skip second line but is different enough (the answers there don't explain what I see here) to warrant a separate question.

R似乎跳过了标题行，并将第二(数据)行视为标题:

R seems to skip the header line and treat the second (data) line as header:

R> d <- read.csv(file='/dev/stdin', header=TRUE) 
a,b
1,2
3,4
# hit CTRL-D twice here to end the input
# (this is also unexpected:
#  when reading a few lines interactively in bash, one CTRL-D suffices.
#  Why is doing it twice necessary in R?)

R> d
  X1 X2
1  3  4

R> colnames(d)
[1] "X1" "X2"

我找到了一种解决方法:由于默认情况下read.csv具有blank.lines.skip = TRUE，因此我在输入前加上一些空行.开始输入之前的5条空行似乎是使它按预期工作所需的最低要求.顺便说一句:一行包含5个空格的行同样有效，提示需要大约5个字节(或更多)的空白填充:

I found a workaround: since by default read.csv has blank.lines.skip = TRUE, I prefix the input with some blank lines. 5 empty lines before starting the input, seem to be the minimum required to get this to work as expected. BTW: a single line with 5 spaces works just as well, hinting at some 5 byte (or more) required whitespace padding:

R> d <- read.csv(file='/dev/stdin', header=TRUE)





a,b
1,2
3,4
# Enter CTRL-D twice here to mark the end of terminal input

R> d
  a b
1 1 2
2 3 4

R> colnames(d)
[1] "a" "b"

问题:

• 为什么第一个示例无法按预期运行?
• 为什么需要5个空白行或空格(即使4个空格也不够)才能使其正常工作?
• 有没有更好的方法可以直接从终端读取简短的csv代码段? (我知道scan和readLines，但是我的数据已经是csv格式，所以我想使其尽可能简单地读取/解析/分配)

• Why isn't the 1st example working as expected?
• Why are 5 blank lines or spaces needed (even 4 aren't enough) to make it work?
• Is there a better way to reading a short csv snippet directly from the terminal? (I know about scan and readLines, but my data is in csv format already, so I want to make it as simple to read/parse/assign as possible)

推荐答案

我认为您发布的第一个链接中的答案可能实际上是适用的. R似乎在/dev/stdin上创建了一个4字节的缓冲区.另外，如评论中所述，您可以改用stdin，它似乎可以正常工作. (尽管我仍然不明白为什么您必须两次按Ctrl + D).

I think the answer in the first link you posted may actually be applicable. R appears to create a 4 byte buffer on /dev/stdin. Also, as mentioned in the comment, you can use stdin instead, and it appears to work fine. (Although I still don't get why you have to hit Ctrl+D twice).

d <- read.csv(file='stdin', header=TRUE)
a,b
1,2
3,4
# Hit Control+D twice.
> d
  a b
1 1 2
2 3 4

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