Since (still) nobody got check-mark, I assume that you have some practical issue in mind, mostly because you haven't specified what type of vector you want to convert to numeric .
(由于（仍然）没有人打勾，因此我认为您会遇到一些实际问题，主要是因为您尚未指定要将哪种类型的向量转换为numeric 。)
I suggest that you should apply transform function in order to complete your task. (我建议您应该应用transform功能以完成任务。)
Now I'm about to demonstrate certain "conversion anomaly":
(现在，我将演示某些“转换异常”：)
# create dummy data.frame
d <- data.frame(char = letters[1:5],
fake_char = as.character(1:5),
fac = factor(1:5),
char_fac = factor(letters[1:5]),
num = 1:5, stringsAsFactors = FALSE)
Let us have a glance at data.frame
(让我们看一下data.frame)
> d
char fake_char fac char_fac num
1 a 1 1 a 1
2 b 2 2 b 2
3 c 3 3 c 3
4 d 4 4 d 4
5 e 5 5 e 5
and let us run:
(让我们运行：)
> sapply(d, mode)
char fake_char fac char_fac num
"character" "character" "numeric" "numeric" "numeric"
> sapply(d, class)
char fake_char fac char_fac num
"character" "character" "factor" "factor" "integer"
Now you probably ask yourself "Where's an anomaly?" (现在您可能会问自己： “哪里有异常？”)
Well, I've bumped into quite peculiar things in R, and this is not the) most confounding thing, but it can confuse you, especially if you read this before rolling into bed. (嗯，我碰到了R中相当独特的东西，而这还不是)最混杂的东西，但它可以迷惑你，特别是如果你滚进睡前阅读。)
Here goes: first two columns are character .
(往前走：前两列是character 。)
I've deliberately called 2 nd one fake_char . (我特意将第二个fake_char 。)
Spot the similarity of this character variable with one that Dirk created in his reply. (发现此character变量与Dirk在他的回复中创建的变量相似。)
It's actually a numerical vector converted to character . (它实际上是一个转换为character的numerical矢量。)
3 rd and 4 th column are factor , and the last one is "purely" numeric . (3 次和第 4列是factor ，最后一个是“纯粹的” numeric 。)
If you utilize transform function, you can convert the fake_char into numeric , but not the char variable itself.
(如果您使用transform功能，则可以将fake_char转换为numeric ，但不能转换为char变量本身。)
> transform(d, char = as.numeric(char))
char fake_char fac char_fac num
1 NA 1 1 a 1
2 NA 2 2 b 2
3 NA 3 3 c 3
4 NA 4 4 d 4
5 NA 5 5 e 5
Warning message:
In eval(expr, envir, enclos) : NAs introduced by coercion
but if you do same thing on fake_char and char_fac , you'll be lucky, and get away with no NA's:
(但是，如果您对fake_char和char_fac做同样的事情，您会很幸运，并且没有NA：)
> transform(d, fake_char = as.numeric(fake_char),
char_fac = as.numeric(char_fac))
char fake_char fac char_fac num
1 a 1 1 1 1
2 b 2 2 2 2
3 c 3 3 3 3
4 d 4 4 4 4
5 e 5 5 5 5
If you save transformed data.frame and check for mode and class , you'll get:
(如果保存转换后的data.frame并检查mode和class ，则会得到：)
> D <- transform(d, fake_char = as.numeric(fake_char),
char_fac = as.numeric(char_fac))
> sapply(D, mode)
char fake_char fac char_fac num
"character" "numeric" "numeric" "numeric" "numeric"
> sapply(D, class)
char fake_char fac char_fac num
"character" "numeric" "factor" "numeric" "integer"
So, the conclusion is: Yes, you can convert character vector into a numeric one, but only if it's elements are "convertible" to numeric . (因此，得出的结论是： 是的，您可以将character向量转换为numeric ，但)前提是它的元素可以“转换”为numeric 。))
If there's just one character element in vector, you'll get error when trying to convert that vector to numerical one. (如果向量中只有一个character元素，则尝试将该向量转换为numerical时会出错。)
And just to prove my point:
(只是为了证明我的观点：)
> err <- c(1, "b", 3, 4, "e")
> mode(err)
[1] "character"
> class(err)
[1] "character"
> char <- as.numeric(err)
Warning message:
NAs introduced by coercion
> char
[1] 1 NA 3 4 NA
And now, just for fun (or practice), try to guess the output of these commands:
(现在，仅出于娱乐目的（或练习），尝试猜测以下命令的输出：)
> fac <- as.factor(err)
> fac
???
> num <- as.numeric(fac)
> num
???
Kind regards to Patrick Burns!
(问候帕特里克·伯恩斯！)
=) (=）)
