data set

here are the two files https://dl.dropboxusercontent.com/u/7710864/data/reviews-apr29.csv https://dl.dropboxusercontent.com/u/7710864/data/solutions-apr29.csv

reviews = read.csv("reviews-apr29.csv")
solutions = read.csv("solutions-apr29.csv")
head(reviews, 2)
##   id solution_id reviewer_id      start       stop time_left accept
## 1  1           3          27 1304095698 1304095758      1754      1
## 2  2           4          22 1304095188 1304095206      2306      1
head(solutions,2)
##   id problem_id subject_id      start       stop time_left answer
## 1  1        156         29 1304095119 1304095169      2343      B
## 2  2        269         25 1304095119 1304095183      2329      C
names(reviews)
## [1] "id"          "solution_id" "reviewer_id" "start"       "stop"       
## [6] "time_left"   "accept"

Lets merge

mergeData = merge(reviews, solutions, by.x = "solution_id", by.y = "id" , all=TRUE)

to know the intersections

intersect(names(solutions), names(reviews))
## [1] "id"        "start"     "stop"      "time_left"