将数据框的列强制为数字

Question

I can't get the following formula to coerce selected columns of a data frame to numeric

x<-read.csv("more.csv",colClasses="character")

test<-list(more[,10],more[,11],more[,12])
test2<-lapply(test,as.numeric)

But

is.numeric(more[,10])
[1] FALSE

When I use the following formula it works:

more[,10]<-as.numeric(more[,10])

is.numeric(more[,10])
[1] TRUE

I can't make out the error in the first formula used.

Answer 1

Because my work doesn't always necessarily use the same column locations, I personally would use a combination of josliber's approach and the original proposal. Create a vector of the column names you want to coerce, and use lapply to modify only those columns.

test <- as.vector(c("test1", "test2", "test3"))
more[test] = lapply(more[test], as.numeric)

Cheers

Answer 2

When you use test2 <- lapply(test, as.numeric) , it is building a new list (called test2 ) with all the elements converted to be numeric. This does not change test and also does not change the data frame more .

You could convert columns 10, 11, and 12 to numeric in your data frame with something like:

more[,10:12] = as.numeric(more[,10:12])

Answer 3

如果as.numeric您也可以使用as.dataframe 。

Answer 4

Assuming your data frame is x and the column name is "value" :

x["value"] <- as.numeric(x[,"value"])

My example won't work if you eliminate the "," in x[,"value"] . I like this method due to its simplicity.