R: Update adjacency matrix/data frame using pairwise combinations - r

Question

Question
Let's say I have this dataframe:
# mock data set
df.size = 10
cluster.id<- sample(c(1:5), df.size, replace = TRUE)
letters <- sample(LETTERS[1:5], df.size, replace = TRUE)
test.set <- data.frame(cluster.id, letters)
Will be something like:
cluster.id letters
<int> <fctr>
1 5 A
2 4 B
3 4 B
4 3 A
5 3 E
6 3 D
7 3 C
8 2 A
9 2 E
10 1 A
Now I want to group these per cluster.id and see what kind of letters I can find within a cluster, so for example cluster 3 contains the letters A,E,D,C. Then I want to get all unique pairwise combinations (but not combinations with itself so no A,A e.g.): A,E ; A,D, A,C etc. Then I want to update the pairwise distance for these combination in an adjacency matrix/data frame.
Idea
# group by cluster.id
# per group get all (unique) pairwise combinations for the letters (excluding pairwise combinations with itself, e.g. A,A)
# update adjacency for each pairwise combinations
What I tried
# empty adjacency df
possible <- LETTERS
adj.df <- data.frame(matrix(0, ncol = length(possible), nrow = length(possible)))
colnames(adj.df) <- rownames(adj.df) <- possible
# what I tried
update.adj <- function( data ) {
for (comb in combn(data$letters,2)) {
# stucked
}
}
test.set %>% group_by(cluster.id) %>% update.adj(.)
Probably there is an easy way to do this because I see adjacency matrices all the time, but I'm not able to figure it out.. Please let me know if it's not clear
Answer to comment
Answer to #Manuel Bickel:
For the data I gave as example (the table under "will be something like"):
This matrix will be A-->Z for the full dataset, keep that in mind.
A B C D E
A 0 0 1 1 2
B 0 0 0 0 0
C 1 0 0 1 1
D 1 0 1 0 1
E 2 0 1 1 0
I will explain what I did:
cluster.id letters
<int> <fctr>
1 5 A
2 4 B
3 4 B
4 3 A
5 3 E
6 3 D
7 3 C
8 2 A
9 2 E
10 1 A
Only the clusters containing more > 1 unique letter are relevant (because we don't want combinations with itself, e.g cluster 1 containing only letter B, so it would result in combination B,B and is therefore not relevant):
4 3 A
5 3 E
6 3 D
7 3 C
8 2 A
9 2 E
Now I look for each cluster what pairwise combinations I can make:
cluster 3:
A,E
A,D
A,C
E,D
E,C
D,C
Update these combination in the adjacency matrix:
A B C D E
A 0 0 1 1 1
B 0 0 0 0 0
C 1 0 0 1 1
D 1 0 1 0 1
E 2 0 1 1 0
Then go to the next cluster
cluster 2
A,E
Update the adjacency matrix again:
A B C D E
A 0 0 1 1 2 <-- note the 2 now
B 0 0 0 0 0
C 1 0 0 1 1
D 1 0 1 0 1
E 2 0 1 1 0
As reaction to the huge dataset
library(reshape2)
test.set <- read.table(text = "
cluster.id letters
1 5 A
2 4 B
3 4 B
4 3 A
5 3 E
6 3 D
7 3 C
8 2 A
9 2 E
10 1 A", header = T, stringsAsFactors = F)
x1 <- reshape2::dcast(test.set, cluster.id ~ letters)
x1
#cluster.id A B C D E
#1 1 1 0 0 0 0
#2 2 1 0 0 0 1
#3 3 1 0 1 1 1
#4 4 0 2 0 0 0
#5 5 1 0 0 0 0
x2 <- table(test.set)
x2
# letters
#cluster.id A B C D E
# 1 1 0 0 0 0
# 2 1 0 0 0 1
# 3 1 0 1 1 1
# 4 0 2 0 0 0
# 5 1 0 0 0 0
x1.c <- crossprod(x1)
#Error in crossprod(x, y) :
# requires numeric/complex matrix/vector arguments
x2.c <- crossprod(x2)
#works fine

Answer 1

Following above comment, here the code of Tyler Rinker used with your data. I hope this is what you want.
UPDATE: Following below comments, I added a solution using the package reshape2 in order to be able to handle larger amounts of data.
test.set <- read.table(text = "
cluster.id letters
1 5 A
2 4 B
3 4 B
4 3 A
5 3 E
6 3 D
7 3 C
8 2 A
9 2 E
10 1 A", header = T, stringsAsFactors = F)
x <- table(test.set)
x
letters
#cluster.id A B C D E
# 1 1 0 0 0 0
# 2 1 0 0 0 1
# 3 1 0 1 1 1
# 4 0 2 0 0 0
# 5 1 0 0 0 0
#base approach, based on answer by Tyler Rinker
x <- crossprod(x)
diag(x) <- 0 #this is to set matches such as AA, BB, etc. to zero
x
# letters
# letters
# A B C D E
# A 0 0 1 1 2
# B 0 0 0 0 0
# C 1 0 0 1 1
# D 1 0 1 0 1
# E 2 0 1 1 0
#reshape2 approach
x <- acast(test.set, cluster.id ~ letters)
x <- crossprod(x)
diag(x) <- 0
x
# A B C D E
# A 0 0 1 1 2
# B 0 0 0 0 0
# C 1 0 0 1 1
# D 1 0 1 0 1
# E 2 0 1 1 0