date         code    var1   var2  var3    category
2016-01-01   AAA        1     2      3    2
2016-02-01   AAA        2     3      3    3
2016-01-01   BBB        1     2      3    1
2016-02-01   BBB        2     3      3    3

formula_lm1 <- category ~ var1 +var2 +var3
f_pglm <- pglm(
    formula_lm1,
    data = test,
    family = ordinal('logit'),
    model = "pooling",
    index = c('code', 'date'),
    print.level = 0,
    method = 'nr'
)
summary(f_pglm)