convert one factor to another in R -

i have dataframe

division | category        |    tools        |    work   b      |    tools   b      |    tools 

both columns factor variables. how convert tools tools?

i tried

df$category <- as.character(df$category) df$category <- lapply(df$category, function(x) { tolower(x) } ) df$category <- as.factor(df$category) 

but last command get:

error in sort.list(y) : 'x' must atomic 'sort.list' have called 'sort' on list? 

what mean?

the error means you've tried factor list, although not in words. triggered because used lapply(), returns list. , in situation as.factor() calls factor(), in turn calls sort.list() here:

## factor() if (missing(levels)) {     y <- unique(x, nmax = nmax)     ind <- sort.list(y)     ... } 

which error occurs.

as.factor(list(1, 2)) # error in sort.list(y) : 'x' must atomic 'sort.list' # have called 'sort' on list? 

long story short, can use tolower() without lapply(), vectorized , character coercion you.

df$category <- factor(tolower(df$category)) df #   division category # 1           tools # 2            work # 3        b    tools # 4        b    tools