R将列类从一个数据帧分配(或复制)到另一个

问题描述

我制作了一个大型数据框(1700 + obs，159个变量)，并带有从网站收集信息的功能.通常，该函数查找某些列的数字值，因此它们是数字.但是，有时它会找到一些文本，然后将整个列转换为文本.我有一个df，其列类正确，并且我想将这些类粘贴"到新的，不正确的df中.举例来说:

I produced a large data frame (1700+obs,159 variables) with a function that collects info from a website. Usually, the function finds numeric values for some columns, and thus they're numeric. Sometimes, however, it finds some text, and converts the whole column to text.I have one df whose column classes are correct, and I would like to "paste" those classes to a new, incorrect df.Say, for example:

dfCorrect<-data.frame(x=c(1,2,3,4),y=as.factor(c("a","b","c","d")),z=c("bar","foo","dat","dot"),stringsAsFactors = F)
str(dfCorrect)
'data.frame':   4 obs. of  3 variables:
 $ x: num  1 2 3 4
 $ y: Factor w/ 4 levels "a","b","c","d": 1 2 3 4
 $ z: chr  "bar" "foo" "dat" "dot"

## now I have my "wrong" data frame:
dfWrong<-as.data.frame(sapply(dfCorrect,paste,sep=""))
str(dfWrong)
'data.frame':   4 obs. of  3 variables:
 $ x: Factor w/ 4 levels "1","2","3","4": 1 2 3 4
 $ y: Factor w/ 4 levels "a","b","c","d": 1 2 3 4
 $ z: Factor w/ 4 levels "bar","dat","dot",..: 1 4 2 3

我想将dfCorrect的每一列的类复制到dfWrong，但是还没有找到如何正确执行的方法.我已经测试过:

I wanted to copy the classes of each column of dfCorrect into dfWrong, but haven't found how to do it properly.I've tested:

dfWrong1<-dfWrong
dfWrong1[0,]<-dfCorrect[0,]
str(dfWrong1) ## bad result
'data.frame':   4 obs. of  3 variables:
 $ x: Factor w/ 4 levels "1","2","3","4": 1 2 3 4
 $ y: Factor w/ 4 levels "a","b","c","d": 1 2 3 4
 $ z: Factor w/ 4 levels "bar","dat","dot",..: 1 4 2 3

dfWrong1<-dfWrong
str(dfWrong1)<-str(dfCorrect)
'data.frame':   4 obs. of  3 variables:
 $ x: num  1 2 3 4
 $ y: Factor w/ 4 levels "a","b","c","d": 1 2 3 4
 $ z: chr  "bar" "foo" "dat" "dot"
Error in str(dfWrong1) <- str(dfCorrect) :
  could not find function "str<-"

有了这个小的矩阵，我可以手工处理，但是较大的矩阵呢?有没有一种方法可以将类从一个df复制到另一个df，而不必知道每一列的各个类(和索引)?

With this small matrix I could go by hand, but what about larger ones? Is there a way to "copy" the classes from one df to another without having to know the individual classes (and indexes) of each column?

预期的最终结果(在正确地粘贴"类之后):

Expected final result (after properly "pasting" classes):

all.equal(sapply(dfCorrect,class),sapply(dfWrong,class))
[1] TRUE

谢谢

推荐答案

您可以尝试以下方法:

dfWrong[] <- mapply(FUN = as,dfWrong,sapply(dfCorrect,class),SIMPLIFY = FALSE)

...虽然我的本能是同意奥利弗(Oliver)的看法，但如果是我，我会尽力确保在读取数据时使用正确的课程.

...although my first instinct is to agree with Oliver that if it were me I'd try to ensure the correct class at the point you're reading the data.

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