[R] Compare two data frames

[Doran, Harold]

I wonder if there is a more efficient way to do this task. Suppose I have two data frames, such as

d1 <- data.frame(x = c(1,2,3), y = c(4,5,6), z = c(7,8,9))

d2 <- d1[, c('y', 'x')]

The first dataframe d1 has more variables than d2 and the variable columns are in a different order.

So, what I want to do is compare the two frames on the variables that are common between the two. First I find the common variables between the two dataframes

common_order <- intersect(colnames(d1), colnames(d2))

Then, I have to put the variables in d2 in the same order as d1 as

d2 <- d2[, common_order]

Then, I keep only the variables in common between d1 and d2 as

d1 <- d1[, common_order]

Then, finally I can do the compare on the common variables now in the same order.

all.equal(d1, d2)

None of this is horribly difficult, but it requires a couple of steps that I am wondering might be eliminated. 

Harold

> sessionInfo()
R version 2.10.1 (2009-12-14) 
i386-pc-mingw32 

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252    LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C                           LC_TIME=English_United States.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] MiscPsycho_1.6 statmod_1.4.6 

loaded via a namespace (and not attached):
[1] tools_2.10.1