Setting incomparables in place with merge

Question

I'm seeing some unexpected behaviour with merge (or at least not entirely intuitive). But perhaps I'm just not understanding how it's supposed to work:

Let's create some dummy data to play with first:

x <- structure(list(A = c(2L, 2L, 2L, 2L, 1L, 2L, 1L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 2L), B = c(2L, 2L, 1L, 2L, 
1L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 1L, 2L, 1L, 1L, 2L, 2L, 1L, 1L
), C = c(2L, 1L, 2L, 1L, 2L, 1L, 1L, 2L, 2L, 2L, 2L, 1L, 2L, 
2L, 1L, 1L, 1L, 1L, 2L, 2L), D = c(2L, 1L, 2L, 2L, 2L, 1L, 1L, 
2L, 1L, 2L, 1L, 2L, 1L, 1L, 2L, 1L, 2L, 1L, 1L, 1L), E = c(2L, 
1L, 1L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 
1L, 1L, 1L), F = c(1L, 1L, 1L, 1L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 
2L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L), G = c(2L, 2L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 2L), 
    H = c(1L, 2L, 1L, 2L, 1L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 
    1L, 2L, 1L, 2L, 1L, 1L, 1L), I = c(1L, 1L, 2L, 2L, 2L, 1L, 
    1L, 1L, 2L, 1L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 2L, 1L), 
    J = c(2L, 1L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 
    2L, 2L, 2L, 2L, 1L, 2L, 1L), K = c(3, 3, 1, 3, 1, 3, 1, 2, 
    2, 2, 1, 3, 2, 2, 2, 1, NA, 1, 2, 1)), .Names = c("A", "B", 
"C", "D", "E", "F", "G", "H", "I", "J", "K"), row.names = c(NA, 
20L), class = "data.frame")

# Generate Listing of All Possible Combinations 
y <- list(1:2); y = expand.grid(rep(y,10)); 
colnames(y) <- LETTERS[1:10]
y <- rbind(y,y,y)
y$K <- rep(1:3,each=1024)
y$mergekey <- sample(1:6,3072,replace=TRUE) 

My expectation is that when I merge these two data sets that setting sort=FALSE and all.x=TRUE would provide me with a list of all x in place with mergekey.

Let's try that:

merge(x,y,all.x=TRUE,sort=FALSE)
   A B C D E F G H I J  K mergekey
1  2 2 2 2 2 1 2 1 1 2  3        5
2  2 2 1 1 1 1 2 2 1 1  3        3
3  2 1 2 2 1 1 2 1 2 2  1        3
4  2 2 1 2 2 1 2 2 2 2  3        2
5  1 1 2 2 2 2 2 1 2 2  1        4
6  2 1 1 1 2 2 2 2 1 2  3        6
7  1 1 1 1 2 2 2 2 1 2  1        5
8  2 1 2 2 1 1 2 2 1 1  2        4
9  2 2 2 1 1 1 2 1 2 2  2        4
10 2 1 2 2 1 1 2 1 1 1  2        2
11 2 1 2 1 1 1 2 1 2 2  1        4
12 2 2 1 2 1 2 2 1 2 1  3        5
13 2 1 2 1 1 1 2 1 2 2  2        3
14 2 1 2 1 1 1 2 1 2 2  2        3
15 2 2 2 1 2 1 2 1 2 2  2        1
16 2 1 1 2 1 1 2 2 2 2  2        1
17 2 1 1 1 1 1 2 1 1 2  1        2
18 1 2 1 1 1 2 2 1 1 1  1        5
19 2 1 2 1 1 1 2 1 1 1  1        4
20 2 2 1 2 1 1 1 2 1 2 NA       NA

Now it seems that "most of x is unsorted" but incomparables are pushed to the end, rather than maintaining their order.

So, my question is: How do I get the incomparables to stay in place?

PS: Does it not seem a little unintuitive to push incomparables to the end if the merge has been told not to sort? I don't find this congruent with this behaviour either

Answer 1

The join function in the plyr package solves this problem intuitively without additional arguements.

library(plyr)
join(x,y)

Joining by: A, B, C, D, E, F, G, H, I, J, K
   A B C D E F G H I J  K mergekey
1  2 2 2 2 2 1 2 1 1 2  3        4
2  2 2 1 1 1 1 2 2 1 1  3        3
3  2 1 2 2 1 1 2 1 2 2  1        5
4  2 2 1 2 2 1 2 2 2 2  3        3
5  1 1 2 2 2 2 2 1 2 2  1        6
6  2 1 1 1 2 2 2 2 1 2  3        6
7  1 1 1 1 2 2 2 2 1 2  1        4
8  2 1 2 2 1 1 2 2 1 1  2        2
9  2 2 2 1 1 1 2 1 2 2  2        4
10 2 1 2 2 1 1 2 1 1 1  2        6
11 2 1 2 1 1 1 2 1 2 2  1        1
12 2 2 1 2 1 2 2 1 2 1  3        3
13 2 1 2 1 1 1 2 1 2 2  2        2
14 2 2 2 1 2 1 2 1 2 2  2        6
15 2 1 1 2 1 1 2 2 2 2  2        2
16 2 1 1 1 1 1 2 1 1 2  1        3
17 2 2 1 2 1 1 1 2 1 2 NA       NA
18 1 2 1 1 1 2 2 1 1 1  1        1
19 2 1 2 1 1 1 2 1 2 2  2        2
20 2 1 2 1 1 1 2 1 1 1  1        1