if/else statement evaluating only else statement

Disclaimer: This is a question regarding an assignment for a Coursera course.

I'm having trouble coming up with a way to create a new column that differentiates between weekdays and weekends in my data set. I'm using a nested if/else statement within a for loop. The problem is the output makes every row 'weekday'. Does anyone see something glaringly wrong with my code? My end goal is to create a new factor variable that is either "weekend" or "weekday."

df4 <- mutate(df4, day = weekdays(df4$date))
for (i in df4$day) {
    if(i %in% c("Saturday",'Sunday')) {
        df4$day_type <- 'weekend'
    } else {
        df4$day_type <- 'weekday'
    }
}