如何从R向量的每个元素中去除最后的n个字符

I am very new to R, and I could not find a simple example online of how to remove the last n characters from every element of a vector (array?)

我对R很陌生，我在网上找不到一个简单的例子来说明如何从向量的每个元素(数组?)中删除最后的n个字符。

I come from a Java background, so what I would like to do is to iterate over every element of a$data and remove the last 3 characters from every element.

我来自Java背景，所以我想做的是遍历$data的每个元素，并从每个元素中删除最后3个字符。

How would you go about it?

你会怎么做?

4 个解决方案

#1

Here is an example of what I would do. I hope it's what you're looking for.

这是我要做的一个例子。我希望这就是你要找的。

char_array = c("foo_bar","bar_foo","apple","beer")
a = data.frame("data"=char_array,"data2"=1:4)
a$data = substr(a$data,1,nchar(a$data)-3)

a should now contain:

现在应该包含:

  data data2
1 foo_ 1
2 bar_ 2
3   ap 3
4    b 4

#2

Here's a way with gsub:

这里有一个关于gsub的方法:

cs <- c("foo_bar","bar_foo","apple","beer")
gsub('.{3}$', '', cs)
# [1] "foo_" "bar_" "ap"   "b"

#3

The same may be achieved with the stringi package:

stringi包也可以实现同样的目标:

library('stringi')
char_array <- c("foo_bar","bar_foo","apple","beer")
a <- data.frame("data"=char_array, "data2"=1:4)
(a$data <- stri_sub(a$data, 1, -4)) # from the first to the last but 4th char
## [1] "foo_" "bar_" "ap"   "b"

#4

Although this is mostly the same with the answer by @nfmcclure, I prefer using stringr package as it provdies a set of functions whose names are most consistent and descriptive than those in base R (in fact I always google for "how to get the number of characters in R" as I can't remember the name nchar()).

虽然这是主要由@nfmcclure相同的答案,我更喜欢使用stringr的包,因为它provdies一组函数的名字是最一致的和描述性的比基R(事实上我总是谷歌“如何得到的字符数R”我不记得这个名字nchar())。

library(stringr)
str_sub(iris$Species, 1, str_length(iris$Species)-3)

This removes the last 3 characters from each value at Species column.

这将从Species列的每个值中删除最后3个字符。

#1