supply a vector to “classes” of dataframe

Question

You know how you can supply a vector of names to a data frame to change the col or row names of a dataframe. Is there a similar method to supply a vector of names that alte

Answer 1

It seems class(x) <- "factor" doesn't work and neither does as(x, "factor"), so I don't know of a direct way of doing what you want.

...But a slightly more explicit way is:

# Coerces data.frame columns to the specified classes
colClasses <- function(d, colClasses) {
    colClasses <- rep(colClasses, len=length(d))
    d[] <- lapply(seq_along(d), function(i) switch(colClasses[i], 
        numeric=as.numeric(d[[i]]), 
        character=as.character(d[[i]]), 
        Date=as.Date(d[[i]], origin='1970-01-01'), 
        POSIXct=as.POSIXct(d[[i]], origin='1970-01-01'), 
        factor=as.factor(d[[i]]),
        as(d[[i]], colClasses[i]) ))
    d
}

# Example usage
DF <- as.data.frame(matrix(rnorm(25), 5, 5))
DF2 <- colClasses(DF, c(rep("character", 3), rep("factor", 2)))
str(DF2)

DF3 <- colClasses(DF, 'Date')
str(DF3)

A couple of things: you can add more cases as needed. And the first line of the function allows you to call with a single class name. The last "default" case of the switch calls the as function and you mileage might vary.