Change part of data frame to character, then to numeric in R

Question

I have a simple problem. I have a data frame with 121 columns. columns 9:121 need to be numeric, but when imported into R, they are a mixture of numeric and integers and factors. Columns 1:8 need to remain characters.

I've seen some people use loops, and others use apply(). What do you think is the most elegant way of doing this?

Thanks very much,

Paul M

Answer 1

Try the following... The apply function allows you to loop over either rows, cols, or both, of a dataframe and apply any function, so to make sure all your columns from 9:121 are numeric, you can do the following:

table[,9:121] <- apply(table[,9:121],2, function(x) as.numeric(as.character(x)))
table[,1:8] <- apply(table[,1:8], 2, as.character)

Where table is the dataframe you read into R.

Briefly I specify in the apply function the table I want to loop over - in this case the subset of your table we want to make changes to, then we specify the number 2 to indicate columns, and finally give the name of the as.numeric or as.character functions. The assignment operator then replaces the old values in your table with the new ones of correct format.

-EDIT: Just changed the first line as I recalled that if you convert from a factor to a number, what you get is the integer of the factor level and not the number you think you are getting to factors first need to be converted to characters, then numbers, which was can do just by wrapping as.character inside as.numeric.

Answer 2

当您在表中阅读时，使用strinsAsFactors=FALSE则不会有任何因素。