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I have a data frame that is 100 X 100. There are 30 columns that are factors. Is there a way to switch only factor-type columns to numeric type without affecting the other columns (without going the loop route)?
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Use the lapply() Function to Convert Multiple Columns From Integer to Numeric Type in R. Base R's lapply() function allows us to apply a function to elements of a list. We will apply the as. numeric() function.
To convert all the columns of the data frame to numeric in R, use the lapply() function to loop over the columns and convert to numeric by first converting it to character class as the columns were a factor.
We must first convert the factor vector to a character vector, then to a numeric vector. This ensures that the numeric vector contains the actual numeric values instead of the factor levels.
Applying the wisdom from Carl Witthoft above:
asNumeric <- function(x) as.numeric(as.character(x))
factorsNumeric <- function(d) modifyList(d, lapply(d[, sapply(d, is.factor)],
asNumeric))
Example:
d <- data.frame(x=factor(1:3), y=factor(2:4), z=factor(3:5),
r=c("a", "b", "c"), stringsAsFactors=FALSE)
> f <- factorsNumeric(d)
> class(f$x)
[1] "numeric"
> class(f$r)
[1] "character"
See R-FAQ 7.10 at cran.r-project.org http://cran.r-project.org/doc/FAQ/R-FAQ.html#How-do-I-convert-factors-to-numeric_003f
ALWAYS do as.numeric(as.character(some_Factor)) or you will be sorry.
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