Test for set inclusion and processing data simultaneously in tidyverse

Question

I almost have what I need. I need some help with the last detail! The data set is produced by the following:

stu_vec <- c("A","B","C","D","E","F","G","H","I","J")
college_vec <- c("ATC","CCTC","DTC","FDTC","GTC","NETC", "USC", "Clemson", "Winthrop", "Allen")
sctcs <- c("ATC","CCTC","DTC","FDTC","GTC","NETC")
Student <- sample (stu_vec, size=100,replace=T, prob=c(.08,0.09,0.06,.07,.12,.10,.07,.05,.11,.05))
College <- sample(college_vec, size=100, replace=T,prob=c(.08,.07,.13,.12,.11,.06,.05,.08,.02,.08))

test.dat1 <- as.data.frame(cbind(Student, College))

I am using the following code to create what I need

library(dplyr)

set.seed(29)
test.dat2 <- test.dat1 %>% 
  group_by(Student, .drop=F) %>% #group by student
  mutate(semester= sequence(n())) %>% #set semester sequence
  summarise(home_school= College[min(which(College %in% sctcs))], # Find first college in sctcs
            seq_home=min(which(College %in% sctcs)), # add column of sequence values
            new_school= if_else(n_distinct(College) > 1, 
            first(College[!(College %in% sctcs) & semester > seq_home]), last(College))) #new_school should be the first non-sctcs school after the sctcs school is found or the last school for that student. 

it produces the following table

I want the NA's to be filled in with the last college for that student. I don't know how to get rid of the NA's. If you know an easier way to produce the same thing please share the knowledge.

Answer 1

It's not clear what you're trying to do. But when [!(College %in% sctcs) & semester > seq_home] returns FALSE, College[!(College %in% sctcs) & semester > seq_home] returns a zero-length character vector, so first(College[!(College %in% sctcs) & semester > seq_home]) returns NA.

When there are no TRUE values in [!(College %in% sctcs) & semester > seq_home], it's because there are no non-sctcs colleges in any of the semesters after semester[seq_home]. If a student transfers from home_school to one or more sctcs schools, but never to any non-sctcs schools, you'll get an NA value.

You're effectively asking the wrong question. I'm not sure what question you're trying to ask, but what you're currently asking is:

What's the first non-sctcs school this student attended after they attended their first sctcs school?

Some students, however, never attend a non-sctcs school after attending their first sctcs school. For this reason, you get an NA response, which is the correct answer to the question.