How to merge two data frames on common columns in R with sum of others?

Question

R Version 2.11.1 32-bit on Windows 7

I got two data sets: data_A and data_B:

data_A

USER_A USER_B ACTION
1      11     0.3
1      13     0.         


        

Answer 1

I wrote the package safejoin which solves this very succintly :

# devtools::install_github("moodymudskipper/safejoin")
library(safejoin)
safe_left_join(data_A,data_B, by = c("USER_A", "USER_B"), 
               conflict = ~ .x+ ifelse(is.na(.y),0,.y))
#   USER_A USER_B ACTION
# 1      1     11   0.30
# 2      1     13   0.42
# 3      1     16   0.63
# 4      1     17   0.26
# 5      2     11   0.39
# 6      2     14   0.28

In case of conflict, the function fed to the conflict argument will be used on pairs of conflicting columns