如何将数据帧列转换为数字类型?
16条回答 默认 最新
- local-host 2010-02-19 00:31关注
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
. I suggest that you should applytransform
function in order to complete your task.Now I'm about to demonstrate certain "conversion anomaly":
# 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
> 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:
> 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?" 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.
Here goes: first two columns are
character
. I've deliberately called 2nd onefake_char
. Spot the similarity of thischaracter
variable with one that Dirk created in his reply. It's actually anumerical
vector converted tocharacter
. 3rd and 4th column arefactor
, and the last one is "purely"numeric
.If you utilize
transform
function, you can convert thefake_char
intonumeric
, but not thechar
variable itself.> 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
andchar_fac
, you'll be lucky, and get away with no NA's:> 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 formode
andclass
, you'll get:> 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 anumeric
one, but only if it's elements are "convertible" tonumeric
. If there's just onecharacter
element in vector, you'll get error when trying to convert that vector tonumerical
one.And just to prove my point:
> 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:
> fac <- as.factor(err) > fac ??? > num <- as.numeric(fac) > num ???
Kind regards to Patrick Burns! =)
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