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

Here's a different approach using ddply :

# requires the plyr package
library(plyr)

# Your example dataframe with added lines
schoolex <- data.frame(userid = c(167, 167, 200, 203, 203), facultyid = c(265, 71111, 200, 300, NA), 
                        courseid = c(NA, 301, 302, 303, 303), schoolid = c(1678, NA, 1678, NA, 1678))

schoolex_duprm <- ddply(schoolex, .(userid), summarize, facultyid2 = facultyid[!is.na(facultyid)][1], 
                               courseid2 = courseid[!is.na(courseid)][1], 
                               schoolid2 = schoolid[!is.na(schoolid)][1])