How can I combine rows within the same data frame in R (based on duplicate values under a specific column)?

Question

Sample of 2 (made-up) example rows in df:

userid   facultyid  courseid schoolid
167       265        NA       1678  
167       71111      301      NA
         


        

Answer 1

aggregate(x = df1, by = list(df1$userid), FUN = function(x) na.omit(x)[1])[,-1]

or use dplyr library:

library(dplyr)

df1 %>%
  group_by(userid) %>%
  summarise_each(funs(first(na.omit(.))))