Merging data by 2 variables in R - r

Question

I am attempting to merge two data sets. In the past I have used merge() with by equal to the variable I want to merge by. However, now I would like to do so with two variables. My first data set looks something like this:
Year Winning_Tm Losing_Tm
2011 Texas Washington
2012 Alabama South Carolina
2013 Tennessee Texas
Then I have another data set with a rank of each team (this is very simplified) for each year. Like this:
Year Team Rank
2011 Texas 32
2011 Washington 34
2012 South Carolina 45
2012 Alabama 12
2013 Texas 6
2013 Tennessee 51
I would like to merge them so I have a data set that looks like this:
Year Winning_Tm Winning_TM_rank Losing_Tm Losing_Tm_rank
2011 Texas 32 Washington 34
2012 Alabama 12 South Carolina 45
2013 Tennessee 51 Texas 6
My hope is that there is a simple way to do this but it may be more complicated. Thanks!

Answer 1

I reproduced your data (try to include a dput of it next time):
A <- data.frame(
Year = c(2011, 2012, 2013),
Winning_Tm = c("Texas","Alabama","Tennessee"),
Losing_Tm = c("Washington","South Carolina", "Texas"),
stringsAsFactors = FALSE
)
B <- data.frame(
Year = c("2011","2011","2012","2012","2013","2013"),
Team = c("Texas","Washington","South Carolina","Alabama","Texas","Tennessee"),
Rank = c(32,34,45,12,6,51),
stringsAsFactors = FALSE
)
You can melt the first dataframe using the reshape2 package:
library(reshape2)
A <- melt(A, id.vars = "Year")
names(A)[3] <- "Team"
Now it looks like this:
> A
Year variable Team
1 2011 Winning_Tm Texas
2 2012 Winning_Tm Alabama
3 2013 Winning_Tm Tennessee
4 2011 Losing_Tm Washington
5 2012 Losing_Tm South Carolina
6 2013 Losing_Tm Texas
You can then merge the datasets together by the two columns of interest:
AB <- merge(A, B, by=c("Year","Team"))
Which looks like this:
> AB
Year Team variable Rank
1 2011 Texas Winning_Tm 32
2 2011 Washington Losing_Tm 34
3 2012 Alabama Winning_Tm 12
4 2012 South Carolina Losing_Tm 45
5 2013 Tennessee Winning_Tm 51
6 2013 Texas Losing_Tm 6
Then using the reshape command from base R you can change AB to a wide format:
reshape(AB, idvar = "Year", timevar = "variable", direction = "wide")
The result:
Year Team.Winning_Tm Rank.Winning_Tm Team.Losing_Tm Rank.Losing_Tm
1 2011 Texas 32 Washington 34
3 2012 Alabama 12 South Carolina 45
5 2013 Tennessee 51 Texas 6

Answer 2

Two separate merges. You would need to wrap your list of by variables in c(), and since the variables have different names, you need by.x and by.y. Afterward you could rename the rank variables.
I'll call your data winlose and teamrank, respectively. Then you'd need:
first_merge <- merge(winlose, teamrank, by.x = c('Year', 'Winning_Tm'), by.y = c('Year', 'Team'))
second_merge <- merge(first_merge, teamrank, by.x = c('Year', 'Losing_Tm'), by.y = c('Year', 'Team'))
Renaming the variables:
names(second_merge)[names(second_merge) == 'Rank.x'] <- 'Winning_Tm_rank'
names(second_merge)[names(second_merge) == 'Rank.y'] <- 'Losing_Tm_rank'

Answer 3

If you are familiar with SQL a rather complicated, but fast way to do this all in one step would be:
res <- sqldf("SELECT l.*,
max(case when l.Winning_Tm = r.Team then r.Rank else 0 end) as Winning_Tm_rank,
max(case when l.Losing_Tm = r.Team then r.Rank else 0 end) as Losing_Tm_rank
FROM df1 as l
inner join df2 as r
on (l.Winning_Tm = r.Team
OR l.Losing_Tm = r.Team)
AND l.Year = r.Year
group by l.Year, l.Winning_Tm, l.Losing_Tm")
res
Year Winning_Tm Losing_Tm Winning_Tm_rank Losing_Tm_rank
1 2011 Texas Washington 32 34
2 2012 Alabama South_Carolina 12 45
3 2013 Tennessee Texas 51 6
Data:
df1 <- read.table(header=T,text="Year Winning_Tm Losing_Tm
2011 Texas Washington
2012 Alabama South_Carolina
2013 Tennessee Texas")
df2<- read.table(header=T,text="Year Team Rank
2011 Texas 32
2011 Washington 34
2012 South_Carolina 45
2012 Alabama 12
2013 Texas 6
2013 Tennessee 51")