how to set reference variable in linear regression with categorical predictors in r?

[nbaes]

I am trying to set a reference variable for my linear regression model in R, however the ways I have tried to do so have failed. would anyone have any ideas on what to do next?

Attempt:

df_aas$nas_field <- relevel(df_aas$nas_field, ref = 1)        # Apply relevel function

Error in relevel.default(df_aas$nas_field, ref = 1) :
'relevel' only for (unordered) factors

Final model:

lm_nas <- lm(formula = c_ns2 ~ nas_field, data = df_aas) # reg with dummy var
summary(lm_nas)

Note: outcome variable is continuous; predictors are character (see below):

unique(df_aas$nas_field)
[1] "phys_math_sci" "applied_bio_agr_env_sci" "biomed_sci" "bio_sci"
[5] "eng_applied_sci" "beh_social_sci"

[startz]

Try

df_aas$nas_field <- factor(df_aas$nas_field, ordered = FALSE)

before you relevel and see if it helps.

[nbaes]

thanks so much! so simple and I missed it.

for anyone's future reference, this process worked in the end

df_aas$nas_field <- factor(df_aas$nas_field, ordered = FALSE)
df_aas$nas_field <- relevel(df_aas$nas_field, ref = "phys_math_sci") # make phys_math_sci ref var

lm_nas <- lm(formula = c_ns2 ~ nas_field, data = df_aas) # reg with dummy var
summary(lm_nas)