[R] merging or joining 2 dataframes: merge, rbind.fill, etc.?

[Nordlund, Dan (DSHS/RDA)]

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Anika Masters
> Sent: Tuesday, February 26, 2013 10:56 AM
> To: r-help at r-project.org
> Subject: [R] merging or joining 2 dataframes: merge, rbind.fill, etc.?
> 
> #I want to "merge" or "join" 2 dataframes (df1 & df2) into a 3rd
> (mydf).  I want the 3rd dataframe to contain 1 row for each row in df1
> & df2, and all the columns in both df1 & df2. The solution should
> "work" even if the 2 dataframes are identical, and even if the 2
> dataframes do not have the same column names.  The rbind.fill function
> seems to work.  For learning purposes, are there other "good" ways to
> solve this problem, using merge or other functions other than
> rbind.fill?
> 
> #e.g. These 3 examples all seem to "work" correctly and as I hoped:
> 
> df1 <- data.frame(matrix(data=c(7, 99, 12) ,  nrow=1 ,  dimnames =
> list( NULL ,  c('a' , 'b' , 'd') ) ) )
> df2 <- data.frame(matrix(data=c(88, 34, 12, 44, 56) ,  nrow=1 ,
> dimnames = list( NULL ,  c('d' , 'b' , 'x' ,  'y', 'c') ) ) )
> mydf <- merge(df2, df1, all.y=T, all.x=T)
> mydf
> 
> #e.g. this works:
> library(reshape)
> mydf <- rbind.fill(df1, df2)
> mydf
> 
> #This works:
> library(reshape)
> mydf <- rbind.fill(df1, df2)
> mydf
> 
> #But this does not (the 2 dataframes are identical)
> df1 <- data.frame(matrix(data=c(7, 99, 12) ,  nrow=1 ,  dimnames =
> list( NULL ,  c('a' , 'b' , 'd') ) ) )
> df2 <- df1
> mydf <- merge(df2, df1, all.y=T, all.x=T)
> mydf
> 
> #Any way to get "mere" to work for this final example? Any other good
> solutions?

If rbind.fill(df1,df2) works, why do you need to use merge?

Dan

Daniel J. Nordlund
Washington State Department of Social and Health Services
Planning, Performance, and Accountability
Research and Data Analysis Division
Olympia, WA 98504-5204