从 r 中的多个文本文件（可能有不平衡的行列数）中读取前 4 列

Question

我有以下类似文本 (csv) 文件要阅读，其中前四列是我感兴趣的，但之后我有很多垃圾。 我只想将前四列读入 R。

我想要前四列，以便输出（在 excel 中打开的 csv）看起来像：

由于 SO 的限制，我无法粘贴整个文件或附加它。 这是锻炼的较小示例：

type,latitude,longitude,name,link1,
W,43.075319,-89.386145,Mirch Masala,"<just link, jjksskkls  hskks > ","<just link, jjksskkls  hskks > "
W,43.07488,-89.390698,Himal Chuli Restaurant,"<just link, jjksskkls  hskks > ","<just link,  hskks , hsksks  > "
W,43.074887,-89.391011,Chautara Restaurant,"<just link,  hskks , hsksks  > ","<just link, jjksskkls  hskks > "
W,43.092866,-89.351587,Dobhan Restaurant,"<just link, jjksskkls  hskks > ","<just link, jjksskkls , ssjjs hskks > "
W,43.074746,-89.393137,State Street Cash Mart,"<just link, jjksskkls  hskks > ","<just link, jjksskkls , ssjjs hskks > "
W,43.072801,-89.395718,Dotty Dumplings Dowry,"<just link, jjksskkls ,    hskks > ","<just link, jjksskkls , ssjjs hskks > "
W,43.074744,-89.393046,Dobra Tea,"<just link, jjksskkls  hskks > ","<just link, jjksskkls , ssjjs hskks > "
W,43.076372,-89.380231,Hi-Madison,"<just link, jjksskkls  hskks > ","<just link, jjksskkls , ssjjs hskks > "
W,43.019624,-89.421822,Candlewood Suites Fitchburg,"<just link, jjksskkls , ssjjs hskks > ","<just link, jjksskkls , ssjjs hskks > "
W,43.08154,-89.524094,Holiday Inn Hotel & Suites Madison West,"<just link, jjksskkls 100  hskks > ","<just link, jjksskkls , ssjjs hskks > "

在导入到 R 时只读取前四列有什么想法吗？

Answer 1

根据您对问题的评论，您的标题有些误导。 您遇到问题的地方是不知道最终data.frame将具有的确切列数。

从?read.table帮助页面：

count.fields 可用于确定导致错误记录长度报告的读取文件问题

所以，让我们尝试一个不同的答案。

首先，让这代表您的数据：

"W",43.075319,-89.386145,"Mirch Masala","<J, K>"
"W",43.07488,-89.390698,"Himal Chuli Restaurant","<J, K>","<J, K>","<J, K>"
"W",43.074887,-89.391011,"Chautara Restaurant","<J, K>","<J, K>"
"W",43.092866,-89.351587,"Dobhan Restaurant","<J, K>","<J, K>","<J, K>","<J, K>"
"W",43.074746,-89.393137,"State Street Cash Mart","<J, K>"
"W",43.072801,-89.395718,"Dotty Dumplings Dowry"

（如果这已经保存为文本或 csv 文件，则您不需要下一步，但为了最小的可重现示例......）

将这些行写入文本文件以模拟read.table过程：

writeLines('"W",43.075319,-89.386145,"Mirch Masala","<J, K>"
"W",43.07488,-89.390698,"Himal Chuli Restaurant","<J, K>","<J, K>","<J, K>"
"W",43.074887,-89.391011,"Chautara Restaurant","<J, K>","<J, K>"
"W",43.092866,-89.351587,"Dobhan Restaurant","<J, K>","<J, K>","<J, K>","<J, K>"
"W",43.074746,-89.393137,"State Street Cash Mart","<J, K>"
"W",43.072801,-89.395718,"Dotty Dumplings Dowry"', "myRaggedFile.txt")

这将创建一个“ read.csv ”的文件，以使用read.table或read.csv 。 不过，诀窍是使用count.fields来确定文件应该有多少列。

dat <- read.csv("myRaggedFile.txt", header=FALSE, 
                col.names=1:max(count.fields("myRaggedFile.txt", sep=",")))
dat
#      X1       X2        X3                     X4     X5     X6     X7     X8
# 1     W 43.07532 -89.38614           Mirch Masala <J, K>                     
# 2     W 43.07488 -89.39070 Himal Chuli Restaurant <J, K> <J, K> <J, K>       
# 3     W 43.07489 -89.39101    Chautara Restaurant <J, K> <J, K>              
# 4     W 43.09287 -89.35159      Dobhan Restaurant <J, K> <J, K> <J, K> <J, K>
# 5     W 43.07475 -89.39314 State Street Cash Mart <J, K>                     
# 6     W 43.07280 -89.39572  Dotty Dumplings Dowry            
dat <- dat[1:4] # To keep just the first four columns
## Or, continuing with my original answer:
## read.csv("myRaggedFile.txt", header=FALSE, 
##          col.names=1:max(count.fields("myRaggedFile.txt", sep=",")))[1:4]

Answer 2

当您读入文件时，请使用以下内容：

fist4columns <- read.table("/file/path/filename.csv", header=TRUE, sep=",")[, c(1:4)]