Pergunta
I have a generic question of how to use and manipulate factors. In my work, R often coerces something into a factor because R does not allow different modes in a matrix, but in actuality I would prefer those columns to remain numeric.
When working with such factors I noticed:
When you have two similar factors (e.g all values between 1 and 5) in different columns, coercing the first column factor to a number by as.numeric() works fine. Coercing the second, third or fourth via as.numeric always adds 1 to every "factor". Why?
There seems to be a difference between
https://stackoverflow.com/questions/22381154
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Russiango$V4 <- as.double(go$V4)
AND
go[,4] <- as.numeric(levels(go[,4]))[go[,4]]
Assuming as.double and as.numeric are indeed largely identical, the difference is somewhere else but I don't get it.
Any syntax experts?
Solução
The statement about coercing to factor b/c of matrix requirements is simply wrong. (R matrices are incapable of holding factor variables.) Perhaps you are thinking of a data.frame. As the R FAQ says you need to use:
go$V4 <- as.numeric(as. character(go$V4))
If a numeric vector is concatenated (with c()) to any character vector, it is immediately coerced to "character" mode. If a column in a text field has non-numeric characters in it, the same thing happens on input.
