如何读取数值作为R中的因子？

Question

I have a data frame A which has numeric column like:

zip code
00601
00602
00607

and so on.

If I read this in R using read.csv, they are read as numeric entities. I want them as factors.

I tried converting them back to factor using

A <- as.factor(A)

But this removes starting zeroes and make A like

zip code
601
602
607

I do not want this. I want to save zeroes.

Answer 1

在read.csv调用中使用colClasses以字符或因子读取它们： read.csv(*, colClasses="factor") 。

Answer 2

You may need to add leading zeros - as in this post . This first converts to a character class. Then, you can change this to a factor, which maintains the leading zeros.

Example

A <- data.frame("zip code"=c(00601,00602,00607))
class(A$zip.code) #numeric
A$zip.code <- sprintf("%05d", A$zip.code)
class(A$zip.code) #character
A$zip.code <- as.factor(A$zip.code)
class(A$zip.code) #factor

Resulting in:

> A$zip.code
[1] 00601 00602 00607
Levels: 00601 00602 00607

Writing A as a .csv file

write.csv(A, "tmp.csv")

results in

"","zip.code"
"1","00601"
"2","00602"
"3","00607"

Answer 3

everything without any text qualifier is (attempted to be) read as numeric, so the issue is basically to know how your data (in case 00607 ) is stored on the flat text file. If without text qualifier, you can either follow the suggestion of @Hong Ooi or use

read.csv(*, colClasses="character")

and then convert each column accordingly (in case you don' want/need all of them to factor ). Once you have a character vector (a data.frame column) converting it to factor is just straightforward

> zipCode <- c("00601", "00602", "00607")
> factor(zipCode)
[1] 00601 00602 00607
Levels: 00601 00602 00607