A problem when releveling a factor to the default order?

Question

I have this df

df = data.frame(x = 1:3)

converted to a factor

df$x = factor(df$x)

the levels by default are

str(df)

now let's make level 2 as the reference level

df$x = relevel(df$x,ref=2)

everything till now is ok. but when deciding to make the level 1 again as the default level it's not working

df$x = relevel(df$x,ref=2)

str(df)


df$x = relevel(df$x,ref=1)

str(df)

Appreciatethe help.

On the modified levels try `df$x <- relevel(df$x, ref=2)` again. It takes the second argument, which is obviously changed. — Andre Wildberg, Nov 18 '22 at 15:51

score 2 · Accepted Answer · answered Nov 18 '22 at 15:47

From ?relevel,

     ref: the reference level, typically a string.

I'll key off of "typically". Looking at the code of stats:::relevel.factor, one key part is

    if (is.character(ref)) 
        ref <- match(ref, lev)

This means to me that after this expression, ref is now (assumed to be) an integer that corresponds to the index within the levels. In that context, your ref=1 is saying to use the first level by its index (which is already first).

Try using a string.

relevel(df$x,ref=1)
# [1] 1 2 3
# Levels: 2 1 3
relevel(df$x,ref="1")
# [1] 1 2 3
# Levels: 1 2 3

FYI, this means that your initial `ref=2` is also suspect ... — r2evans, Nov 18 '22 at 16:26

A problem when releveling a factor to the default order?

1 Answers1