R dataframe factors

Question

I want to droplevels a dataframe (please do not mark this question as duplicate :)). Given all the methods available only one works. What am I doing wrong? Example:

> df = data.frame(x = (c("a","b","c")),y=c("d","e","f"))
> class(df$x)
[1] "factor"
> levels(df$x)
[1] "a" "b" "c"

Method 1 not working:

> df1 = droplevels(df)
> class(df1$x)
[1] "factor"
> levels(df1$x)
[1] "a" "b" "c"

Method 2 not working:

> df2 = as.data.frame(df, stringsAsFactors = FALSE) 
> class(df2$x)
[1] "factor"
> levels(df2$x)
[1] "a" "b" "c"

Method 3 not working:

> df3 = df
> df3$x = factor(df3$x) 
> class(df3$x)
[1] "factor"
> levels(df3$x)
[1] "a" "b" "c"

Method 4 finally works:

> df4 = df
> df4$x = as.vector(df4$x)
> class(df4$x)
[1] "character"
> levels(df4$x)
NULL

While working, I think method 4 is the least elegant. Can you help me to debug this? Many thanks

EDIT: Following comments and answers: I want to remove the factor structure from a data frame and not only droplevels

Answer 1

"Dropping levels" refers to getting rid of unused factor levels, but keeping the object as class factor. You're looking for a way to convert all factor columns into character columns:

> df2 = data.frame(lapply(df, 
           function(x) if (is.factor(x)) as.character(x) else x), 
              stringsAsFactors = FALSE)
> lapply(df2, class)
$x
[1] "character"

$y
[1] "character"

> df2
  x y
1 a d
2 b e
3 c f