Sum variable by group and append result

Question

Dataset HAVE is a tibble edgelist of phone call data from the characters of Recess:

Student   Friend       nCalls
TJ        Spinelli                


        

Answer 1

We can group by 'student' and mutate to create the new column

library(dplyr)
df %>%
  group_by(Student) %>%
  mutate(nCallsPerStudent = sum(nCalls))

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Or using base R

df$nCallsPerStudent <- with(df, ave(nCalls, Student, FUN = sum))