Hello
I'm trying to solve this problem without using a for loop but I have so
far failed to find a solution.
I have two matrices of K columns each, e.g. (K=5), and with numbers of
row N_A and N_B respectively
A = (1 5 3 8 15;
2 7 20 11 13;
12 19 20 21 43)
B = (2 6 30 8 16;
3 8 19 11 13)
(the actual matrices have hundreds of thousands of entry, that's why I'm
keen to avoid "for" loops)
And what I need to do is to apply a function which counts the number of
common elements between ANY row of A and ANY row of B, giving a result
like this:
A1 vs B1: 1 # (8 is a common element)
A1 vs B2: 1 # (8 is a common element)
A2 vs B1: 1 # (2 is a common element)
A2 vs B2: 1 # 11, 13 are common elements
Etc.
I've built a function that counts the number of common elements between
two vectors, based on the intersect function in the R manual
common_elements <- function(x,y) length(y[match(x,y,nomatch=0)])
And a double loop who solves my problem would be something like
(pseudo-code)
For(i in 1:N_A){
for(j in 1:N_B){
ce(i,j)=common_elements(a(i),b(j))
}
}
Is there an efficient, clean way to do the same job and give as an
output a matrix N_A x N_B such as that above?
Thanks a lot for your help
Regards
Pietro
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