如何從R中的strsplit（）獲得空的最後一個元素？

Question

我需要處理一些主要是csv的數據。問題在於如果R在行尾（例如，下面示例中的3之後的那個行）結束時忽略逗號。

> strsplit("1,2,3,", ",") 
[[1]] 
[1] "1" "2" "3" 

我想將它作爲[1] "1" "2" "3" NA來代替。我怎樣才能做到這一點？謝謝。

Answer 1

這裏有幾個想法

scan(text="1,2,3,", sep=",", quiet=TRUE) 
#[1] 1 2 3 NA 

unlist(read.csv(text="1,2,3,", header=FALSE), use.names=FALSE) 
#[1] 1 2 3 NA 

---

這些都返回整數向量。你可以用as.character圍繞其中任何讓你在問題中準確顯示輸出：

as.character(scan(text="1,2,3,", sep=",", quiet=TRUE)) 
#[1] "1" "2" "3" NA 

或者，你可以在read.csv指定scanwhat="character"，或colClasses="character"的輸出略有不同

scan(text="1,2,3,", sep=",", quiet=TRUE, what="character") 
#[1] "1" "2" "3" "" 

unlist(read.csv(text="1,2,3,", header=FALSE, colClasses="character"), use.names=FALSE) 
#[1] "1" "2" "3" "" 

您還可以指定na.strings=""以及colClasses="character"

unlist(read.csv(text="1,2,3,", header=FALSE, colClasses="character", na.strings=""), 
     use.names=FALSE) 
#[1] "1" "2" "3" NA 

Answer 2

哈德利的stringi（以前stringr）庫的基本字符串函數一個巨大的進步（全矢量，一致的功能接口）：

require(stringr) 
str_split("1,2,3,", ",") 

[1] "1" "2" "3" "" 

as.integer(unlist(str_split("1,2,3,", ","))) 
[1] 1 2 3 NA 

Answer 3

使用stringi包：

require(stringi) 
> stri_split_fixed("1,2,3,",",") 
[[1]] 
[1] "1" "2" "3" "" 
## you can directly specify if you want to omit this empty elements 
> stri_split_fixed("1,2,3,",",",omit_empty = TRUE) 
[[1]] 
[1] "1" "2" "3"