如何将带有虚拟变量的矩阵（矩形）转换为带有数字的方阵？

Question

I have this situation, in which I have about 200.000 observations ("source") that follow 8 different "target".
If they follow that target is 1 otherwise is 0 like in the simplified example below:

source	target1	target2	target3
source1	1	0	1
source2	0	1	1
source3	1	1	1

Now, I want to know who follow more target and, consequently, how many times a same source follows more than one target, in other words, in each cell I want to know how many times both conditions are verified.
This would be the idea:

(blank)	target1	target2	target3
target1	2	1	2
target2	1	2	2
target3	2	2	3

Answer 1

library(dplyr)
dat <- tibble::tribble(
  ~source,  ~target1,   ~target2,   ~target3,
"source1",  1,  0,  1,
"source2",  0,  1,  1,
"source3",  1,  1,  1)

mat <- dat %>% select(-source) %>% as.matrix()
crossprod(mat)
#>         target1 target2 target3
#> target1       2       1       2
#> target2       1       2       2
#> target3       2       2       3

^{Created on 2022-11-27 by the reprex package (v2.0.1)}