Matching Pairs for R Dataframes - r

Question

I have a data frame that contains the career records of employees in different offices of a large corporations. I want to identify every pair of employees who have shared working experience in a same office. My data frame structure looks like below
Year Office Employee_Name
2011 Logistics Henry
2012 Logistics Henry
2013 HR Henry
2012 Marketing Peter
2013 HR Peter
2014 HR Peter
2015 HR Peter
2010 Logistics Bob
2011 Logistics Bob
2012 Logistics Bob
In the above sample, Henry and Peter worked together in HR in 2013. Henry also worked with Bob in logistics in 2011 and 2012. I want the final results can be something like:
Year_of_shared_experience Person_A Person_B
1 Henry Peter
2 Henry Bob
The order of Person_A and Person_B does not matter (i.e., it can be Henry in Person_A or it can be Peter in Person_A column). Thanks!

Answer 1

You could merge the table with itself (i.e., a "self-join") and then filter out duplicate entries:
# read data
dat = "
Year Office Employee_Name
2011 Logistics Henry
2012 Logistics Henry
2013 HR Henry
2012 Marketing Peter
2013 HR Peter
2014 HR Peter
2015 HR Peter
2010 Logistics Bob
2011 Logistics Bob
2012 Logistics Bob"
dat = read.table(text=dat, header=TRUE)
# self-join
dat = merge(dat, dat, all=TRUE, by=c("Year", "Office"))
# filter out duplicates
dat = dat[dat$Employee_Name.x < dat$Employee_Name.y,]
dat
#> Year Office Employee_Name.x Employee_Name.y
#> 4 2011 Logistics Bob Henry
#> 8 2012 Logistics Bob Henry
#> 12 2013 HR Henry Peter

Answer 2

An option in tidyverse
library(dplyr)
full_join(dat, dat, by = c("Year", "Office")) %>%
filter(Employee_Name.x < Employee_Name.y)